Technical Questions? - Ask MX Tuner

Dec. 01, 2001 By Mark Klein

Mark Klein is ready to answer your technical questions! Mark has extensive experience race tuning off-road motorcycles for local and national races. If you check back through our 1998/99 archives you will see a series called "Dirtbikes 101." Mark brings his expertise to fielding your maintenance and tuning questions.

Submit a Question

No Top End Power
I have a 93 CR 250 that is driving me crazy! I bought the bike it would start up and run good at low RPMs. since then I have resleeved, new piston, rings, new reeds, crank bearings and all new seals and gaskets. guess what? It still runs exactly the same as the day I bought it. I have tried numerous jets thinking it was a jetting problem, I even tried a carb off a different bike [same year] that someone was selling. Too bad I could not of tried the electrical, but he was not going for it. Anyway, is my next move a stator or CDI? I am lost when it comes to electrical stuff .can the stator be tested? I am trying to avoid buying something I don't need. I was told the stator has a low and high-speed coil, my problem maybe. Well any info would be greatly appreciated. Thanks Charlie

Generally speaking, a worn out top end will only run relatively well at higher RPMs. There are specs for checking the ignition system components. There are resistance readings for checking wires going to each component. They will show the wire colors, where to check and what the reading should be. But be careful. The readings should be taken with a grain of salt. If a spec is for say, 250 ohms and you get 255 ohms, that doesn't necessarily rule that component as being "bad". And by the same token, if it reads dead within the spec range, that doesn't mean the component is good. It still might be faulty. The only true way to check an ignition component is to swap it with a known good unit.

MX Tuner

Hard Starting CR
Hello, I have a recently purchased 1989 Honda CR250. I'm new to the sport but learn very fast. My problem is the bike, if it will start, runs great, very fast.


  • fouling of plugs (NGK B8EG)
    getting started
    erratic idle when warm (very high it seems to me)

New guy solutions:

  • cleaned air filter
    replaced crankcase oil
    turned idle down
    replaced several plugs (all the same)
    cleaned and lubed every moving part I can think of

I can kick all day sometimes and nothing. I will let it sit for a day and 3 or 4 kicks and it starts right up. I run 40:1 gas mix. It has a FMF expansion chamber and spark arrestor. I believe everything else is stock. That's what the previous owner told me anyway. I have decent mechanical skills with autos but never have worked on a bike. The bike has been ridden a lot it looks like. I know it needs work but where do I start to get it to consistently start. I know there are probably a few hundred things to look for first, all I'm asking for is a few. Thanks for your time.

Geoff - Southeastern Michigan

Your starting technique may need some fine-tuning. Sounds like you have either an air leak, some carburetor jetting issues or a combination of both. Once you get these issues straightened out, you should be able to develop a normal starting procedure.

You need to check for an air leak. Do this by spraying some carb cleaner around suspect areas while the bike is running as close to idle as possible. Areas to check are the left side crank seal (under the flywheel- spraying under the flywheel will give an indication if the seal is leaking), the cylinder base gasket and the intake manifold area. If you get an increase in speed with the carb cleaner, you have a leak that needs to be repaired. A good starting place for jetting is back to stock. Your local Honda dealer should be able to give you the stock specs. Once you get the erratic running sorted out, you can fine-tune the jetting for optimum throttle response.

MX Tuner

Misfiring When Hot
Mark, I have a 84 CR500 that's runs good for a couple of hard passes then starts to misfire and pop till it shuts down. Trying to restart it gets the same results. Had CDI, stator, coil and p/u ohms checked. Told they were ok. This was done couple days later. Reeds ok jetting ok not clogged or anything. Any ideas other than buying each ignition part one by one.



The resistance checks the manual gives are to be taken with a grain of salt. The fact that it runs normally, and as it heats up starts misfiring, tells me the electrical components should be checked in a failed state. In other words, with the components cold, they'll check fine. Besides, even if they check okay at operating temp, that doesn't mean they are okay. Resistance values are meant to be a diagnostic aid but not an absolute test. Even if you get a reading out of specs, that doesn't mean that part is causing the problem. Make sure all the ground points of all the components are clean and free of corrosion (coil mounting tabs, etc).

MX Tuner

Are All 250R Cylinders Interchangeable?
I am working on a 1985 ATC 250R and it needs a new cylinder. I have one off of a TRX250R lying around extra and I am trying to figure out if it will bolt right on to my ATC. The boltholes and everything match right up but I have heard that the bore, stroke and port timing could be different.

What I'm wanting to know is this:

  • Can I use this cylinder without getting a different rod?

  • Do I need to add a spacer plate of some sort to make the cylinder length work out?

  • Will the port timing radically change my performance?

Thanks for any and all help.


I'd check the replacement crank or rod kits (OEM and aftermarket) to see if they are the same. I'm not sure of the ATV's, but the CR cranks are the same for a number of years. This should give a good indication of the interchangeability. If the port timing is different, and that's the only difference, it'll give the power delivery characteristics of that cylinder.

MX Tuner

Mal Malaguti
Hi, Not sure if u deal with Kids MX but here goes... I have a Malaguti Grizzly 12 (50cc) which my 10yr old daughter rides in the Dubai MX Series, it seems to be a bit flat out of corners, the KTMs etc really punch out whilst the Grizzly seems to be constant, this makes it easy to ride but loses ground out of corners. Any tuning suggestions? It's an auto so this limits the options.

Thanks In Advance


There isn't a heck of a lot that can easily be done to the 50cc racers. Make sure the jetting is as close to optimum as you can get. You can have some porting/compression mods done to get more power but they may sacrifice some reliability and make it even harder to tune.

MX Tuner

Non-Idling XR
Hi, I have a 1984 XR 250. It starts easy and runs well, but after riding a while I drop down to idle and it doesn't idle for long and sometimes doesn't idle at all, it just cuts. I warm it up on choke when I start it and it idles longer, but will still cut. I have had it tuned up but it is still not fixed. I asked the dealer if the idle was too low but he said if that was the problem it wouldn't idle at all. What should I do?

Thanks, Alex

Get a new dealer. Sounds too much like an air leak to miss this. Is your XR a dual carb model? If so the carb set up is difficult to do correctly and can give a variety of symptoms. These are the two directions I'd pursue.

MX Tuner


Leaking 1999 RM 125
I have a leak (very slow) between the block and the inner case cover on the clutch side of the bike. I have purchased the gasket to be replaced and I would like to know if there are any specific torque patterns to follow and what lbs. should they be tightened to when I reinstall the case cover?

I would look at the book, but I bought the bike used and it did not come with one...

Any recommendation is appreciated...

A manual is the first thing I'd buy for your bike. It is full of info you'll need. The torque specs for the case screws is 7lb/ft. I'd snug them all up first and then tighten them in a circular pattern. You won't need to go in a criss-cross pattern.

MX Tuner

Frame Fell Off
Hello, In February or so I purchased a 1990 Suzuki RM80. Bike has been trouble ever since. Once we got the thing running good it was perfect for me, I didn't do any racing, but I did do a small amount of jumping, but nothing heavy. About a month or so I took it for a ride out in the country cause I was bored. Came home after about a 20-25 minute ride and didn't notice a thing. The next day or two I just glanced at the bike and noticed something odd, something very odd. A piece of the frame that runs from the foot peg up underneath the seat was completely missing, only thing left behind was a little rust. So by my guess it had been cracked for quite some while before it had fallen off.

My question is, is there anyone that manufactures just sections of frames that you can buy, or just the whole frame. Would this just be expensive? For what years was the frame made? Any help would be greatly appreciated.


A frame will be almost cost prohibitive for that bike. I'd suggest going to a good welding shop and have them weld in a new tube. It doesn't have to match the exact bend as the original but just strengthen it adequately to be safe. You can even get the original color frame paint from PJ-1 to make it match the rest of the frame.

MX Tuner

1979 Yamaha MX 100
My brother and I are having problems with the piston size. We bought the bike off a friend and he did not have the manual. We would like to know what is the regular size piston that goes with the bike, as I cannot find the exact year it was made in on the Internet. We've tried to figure out what size the piston is, but to no avail. Please help with the piston size. Thank you.

All the YZ 100's had a bore of 50.00 mm from the factory. Wiseco makes original and oversized pistons for your bike.

MX Tuner

Kickin' KX
I have a 1999 KX250, which I cannot seem so get the suspension smooth, like my friends 2000 KX. The problem I am having is the suspension on the front is rough especially in bumpy terrain. The back is smooth but has a tendency to kick up when ever I jump the bike.

I have messed with the front rebound and dampening a little and done the same with the rear. What setting would be best to try on the front and back or should I change out the stock springs and go with a higher rated spring? I weigh about 185 pounds with equipment on. What should I do?

Your KX came with progressive rate springs from the factory. Most guys replaced the springs with straight rate springs first thing. But I don't think that's your problem when you're on trails. If the fork oil hasn't been changed in a while, I'd definitely do that first. Old oil can make the fork action quite harsh. Doing this would be the first place to start to make the forks plusher.

The kicking sensation in the rear could be the shock rebound set too light. I'd start out with the shock rebound adjuster set at 12 out from fully seated lightly. Make sure the rear spring sag is set to 100mm with you standing on the foot pegs, not sitting on the seat. Start out with the fork clickers set at 14 out for the rebound and 12 out with the compression adjuster with fresh oil. Anything that is going to make it better than that will have to involve a substantial investment in springs and possibly a revalve.

MX Tuner


I Want To Race
I have been playing around on dirt bikes for about 4 years now and currently own 2 bikes, 00 KTM 250 and a 91 KTM 300 EX. I'm starting to feel confident with my riding, taking on hill climbs and average jumps. I have been riding with several experience riders, listening to their advice and following their lines. I'm wanting to do some racing and I'm looking for a good place to start. The local MX tracks around here are way too advanced for my level and I enjoy longer rides. Do they have novice classes for desert racing? Where would be the best/easiest place for me to try a desert race?


Your best bet is to ask around at your local bike shop for some events. You can check the printed copy if Cycle News, in the "calendar" section for races listed according to state and date. Generally speaking, a desert race is more difficult to set up and organize than a local motocross since land permits and permissions need to be granted well in advance. There is a much larger support staff that is required to put on a safe desert event. The "Best In The Desert" is a sanctioning body that holds a few quality events a year, some being quite long (500+ miles). Check their website for some details. Try for more info.

MX Tuner

How do you tell how much oil goes in a RM 125 1996.

A veritable cornucopia of information can be found in the original Suzuki owners manual.

MX Tuner

Editor's note: Generally Suzuki will cast the oil capacity into the side cover near the kick start, it is usually measured in milliliters. Mark is right though – there are excellent tips and tricks in the OEM manual – order one from your local Suzuki dealer.

Bolt On Power?
I have a 2000 Suzuki RM125, and I was wondering how to get more power out of it, with bolt on products. It already has a pipe and silencer, and I was thinking of reeds, but can't decide which to get, for more bottom end snap, (V-Force Delta) or (Boyesen.) I would appreciate any info you could give me on reeds, and other bolt on performance parts.

Thanks, Eric


It's no secret I'm a fan of the V-Force reeds. They provide a big boost in throttle response from low RPMs all the way to a great top end. Remember to rejet to compensate for any reeds you choose to use, or you may be disappointed or just not realize the full benefits available from the reeds. Cometic makes a gasket kit that comes with a thinner base gasket, this is known as their "high performance" top end gasket kit. The thinner base gasket will raise the compression slightly and lower the port heights giving better low and midrange power. A nice benefit when you do your next top end.

MX Tuner

Thinking Of Buying - 1995 Kawasaki KX 125
I hope you can help, I'm thinking of buying the above bike but am a bit worried about a fairly loud rattle coming from the top of the engine. The rattle doesn't get quicker with engine revs, what do you think it could be and would it be expensive to put right? The owner is telling me it's been like it since he has owned it and he thinks it's the reed valve. Apart from this rattle the bike is perfect and in lovely condition, its about 25% cheaper than it should be, Should I buy it???

That is a question I can't answer. I can't imagine a rattle, coming from the top end that doesn't increase with engine RPM. The power valves can make some noise if they are loose or worn, and eventually hit and destroy the piston if not fixed. But even this would most likely follow some pattern that followed engine speed. You're on your own with this one. It might get quite pricey trying to fix this if, or when, it develops into more than a noise.

MX Tuner

Adding A Headlight
I have a TRX90 for my daughter and I would like to put a headlight on it [but] there is no existing light or wires. Does it have a lighting coil or an alternator? Please explain how! THANK-YOU Gary

You need to install a lighting coil. This lives behind the flywheel on the left side of the crankshaft. I'd contact a company who does specialty electrical work like winding coils for that bike. Try looking in the back of a printed issue of Cycle News. They have an ad section with countless ads from aftermarket companies. Look for one called "Ricky Stator". I've heard good things about them and their service.

MX Tuner

Top End Rattler
I own a 2000 CR500. The top end is starting to rattle just a little bit. I do all of my own work, but this is my first 2-stroke in 10 years. I was wondering if there is a better piston and ring kit than stock. I have done the proper jetting to match my FMF pipe & silencer, I have also added the moose manifold spacer and changed the air filter assembly. The bike runs awesome the way it is and I just want to freshen it up with the best parts. I don't race it I trail ride it with the occasional blast on a fire road or across an open field. I mix my fuel at 40:1 with Sunoco 94 and Yamalube 2-R oil and never have a problem at all with my bike. Any input would be greatly appreciated. Thank you, Dave

You can use either the stock CR piston or any one of a couple aftermarket pistons. If you go with an aftermarket piston (and I would), I'd go with the Wiseco. Some of the others are designed to be changed in a very short time span.

MX Tuner

Getting Into Gear
Hi, I own an 86 Kawasaki KX 250 and when the bike idles high it wont go into first gear. When I press down to put it into first it grinds and it just wont go, but if the bike is idling really low (almost stalling) it will go into gear. I tried adjusting the clutch cable but it doesn't seem to do anything. What could this be?? Thanks

Sounds like the clutch isn't releasing fully. This can be caused from anything from transmission oil to a notched clutch basket or hub. The metal plates may also be warped, giving the same symptoms. Use the stock clutch springs instead of the heavy duty springs some people recommend. If the cable is stretching, it can give the same symptoms you have.

MX Tuner


What Bike?
I need a little advice. I have been wanting to get back into off road riding again and I want to know what bike would be best for me. I have not ridden in almost 20 years and from what I am seeing a lot has changed. I used to ride a YZ80 and then stepped up to a YZ100. But since the YZ100 I have not ridden at all. I got on a YZ426F and it scared the SHIT out of me. That thing was oozing power.... way to much power for me. I would like to find a bike that I can "re-learn" on and still have fun with. I have talked to a few local dealers and it seems like all they have on their mine is making money (duh!) and selling me something that I am not sure I need (like the 426). So, do you have any suggestions? I am 6ft 3in tall and weight about 255lbs. Please help!!!

With you tipping the scales at 255, you need a pretty big bike. If you get anything smaller than a 250, you're going to have places you need more power. The YZ 250 (two stroke version) is an excellent and versatile bike but would have some fairly harsh suspension in stock condition for woods riding. I think I'd look at a Gas Gas 250 or 300 or a KTM 250 or 300. These are great off-road bikes that have a much more "useable" power output than the 426 you rode. Either 300 would be a great bike you can learn on and not be limited once you get comfortable with it. You'll be able to ride that bike for a long time without worrying about outgrowing it. Gas Gas also makes an excellent off-road bike but there may not be quite as many dealers around for the Gas Gas. One dealer who has outstanding support all over the country is Jim Cook at Smackover Motorsports in Arkansas. He is a rare breed of person and can be trusted to sell you what you need and not what he can make the most money on. He may have a demo or a year old bike for sale. Go to for more info on some excellent bikes.

MX Tuner

84 Honda XR250R
I just put on a new 280 kit and rebuilt the carb to the best of my ability. (There's my first problem, I worked on the bike.) It will start and idle but when I give it any gas it seriously bogs most of the time. The strange thing is occasionally it will hook up and run like it's supposed to. I will be test riding it, it will be totally bogged down, then all of a sudden something pops, and it runs fine for a few minutes. Then it will bog down again. I haven't messed with the jetting yet. I know I have to play with the carb some more but I would think the bogging would be constant. I wouldn't normally ask this type of question except for the fact that it is intermittent.

Thanks. Dan


Sounds like you're on the right track. Check things like the gas cap and carb vent hoses for plugging. These can give some unusual intermittent symptoms. If the float needle is sticking periodically, it can also give some weird symptoms. It may be so work that it is hanging up in the needle seat.

MX Tuner


Pipe Repair (or Pipe Dream)
Hey, I was riding my dirtbike the other day and I fell and smashed my knee into my pipe. I made a dent about 3" wide, and 3" length. I don't want to send it too a business and pay 40$ to get it repaired. If you could, would you tell me how to repair it if you know how too?

Thanks, Dane

Yes, I know how and no, I won't tell you. This is something that can be dangerous at best. The $40 is more than worth it to pay to have it repaired professionally.

MX Tuner


Too Much Stiction
MX Tuner, I have too much stiction in the initial stroke of my fork on my 2000 KTM 300 EXC. I am riding everything from rocks in northern PA to sand in southern NJ. I'm realistic with my speed. I'm not very fast. But I'm no beginner. I guess you would call me a Vet C rider. I'm 6', 225 pounds. It has been revalved with new fork seals, stock fork oil weight, stock springs. I do use a WER stabilizer. What should I do to help my fork?

Thanks Dan

The best thing I can recommend for stiction is an oil additive made by Dow Corning called Gear Guard M. This is a moly disulfide oil additive that works extremely well. Adding about 3ccs per leg will do wonders for your stiction.

MX Tuner

Water In Engine?
Hi, I have a 2001 KLX 300 that I love (with the exception of the powerband but that can be cured later). Anyway, I was riding this last Sunday and all was well until I forded a 2-3 foot deep puddle. Well to make a long story short it sputtered out about 5 minutes later. I rode quickly back to the truck as it sputtered backfired and pinged like crazy. I took the air cleaner off and there was a little water at the very bottom of the airbox but the air cleaner looked intact as far as keeping water out. I took the plug out and moved the piston up and down to see if any water was possible in the head [-] but not that I can tell. I am scared to death I did major damage to the engine but cant know for at least 2-3 weeks because I am too busy to get the bike to the shop and it probably has a total of 30 hours on it only. Is there anything I can do to see for sure in the mean time? Is there something I can do/check to avoid the crazy prices the shop will charge?

Oh yeah I took the air cleaner off and tried starting but it wouldn't start. You could tell it wanted too. I honestly don't know if this is related because sometimes it's a bear to start and I honestly don't know when it will start right up or not. Arghhh!!!! Someone help!

If you got enough water into the motor to do any damage, it would have occurred immediately. If there is any remaining, it may corrode so don't' delay in getting it started again. First thing I'd do is pull the carb apart and clean its internals thoroughly. You might have some water in an electrical connection but they are normally fairly resistant to water.

MX Tuner

Cranking It Up

I have a 1994 RM250 that I am rebuilding. Are aftermarket crank/ rod assemblies worth the money, or is the stock assembly good enough? There is nothing wrong with my crank/rod/bearing assembly, but would the aftermarket bottom end make a noticeable difference in performance/durability? I am a novice and never race the bike; I just use it for a trail/play bike. And could you recommend a good piston manufacturer, or is OEM just fine? And I need a flywheel puller, could you recommend a quality tool company, Snap-On does not make one for my bike.

Thank You - Leo

The aftermarket rod kits are a good quality if installed correctly. If you don't use a stock RM piston, I'd recommend a Wiseco piston kit. The rod kit won't give any increase in power or reliability except from the standpoint that it is new and your existing rod isn't. If you have no perceptible up and down play in your lower end rod bearing, it should be fine for a while. There is also a side clearance you can check to measure the thrust washer wear. Check your manual for exact specs.

Motion Pro makes good quality tools for a decent price. They'll have your flywheel puller at a fraction of the price that Snap-On would if they did make one. Check with your bike dealer for Motion Pro tools.

MX Tuner


KX Fouling
I own a 1998 KX 250 that I recently purchased from a friend. The problem that I am having is fouled plugs. I am an experienced rider, and have no problem staying on the pipe. This past weekend I went riding & had no problem for about two hours of straight riding. We had come off a road with some high speed corners and I had ridden the bike pretty hard down the trail. We slowed down to wait for some of our friends when all of the sudden my plug fouled. I had no warning that this would happen no smoking, loading up etc. The bike was running great and it was like I had depressed the kill button and came to a complete stop. At first, I thought the motor had gone because I have never seen a plug foul like that. From my experience, bikes are usually loaded up and running rough right before a plug fouls. Anyway, my friend gave me a plug on the trail so I tried it. I didn't think it would work but low & behold it fired right up. We rode back to camp and I replaced the loaned plug with my correct plug a BR9EVX. Thinking everything was o.k. we headed back out on the trail. My bike lasted about 30 minutes when the identical thing happened again. No warning just instantly died. I replaced the fouled plug (very black at the tip) with another loaner and went home. Please let me know if you have any idea what is happening. The premix is 32:1 premium pump gas with Maxima 927 oil. I have ridden with the friend that I purchased the bike from many times and this never happened. I have been told spark plug gap, spark plug boot or stator coil could be to blame but I would just like a solid place to start. Your help would be appreciated.

I ran into this exact symptom once with a '96 YZ 250. The thing that fixed the problem was cleaning the coil mounting tabs on the frame. There was paint under the tabs and the coil eventually lost sufficient ground through the bolt threads. It definitely sounds like an electrical problem.

The high dollar plugs aren't helping any, either. I'd use a BR8ES. The 9-heat range plug is one heat range too cold. Stick with the 8 series plug.

MX Tuner

Automatic Clutch
I have seen an automatic clutch for a KX60/65 and don't know where to get one. As of now, I need it to fit a 2001/2 KX65. The assembly allows you to "pin" the transmission in preselected gear and run the bike in that gear and that gear only i.e. 3rd gear. I do know it is an aftermarket part and not available from Kawasaki. Thanks for any help.


Check with Berg Racing for your automatic clutch.

MX Tuner

1976 YZ125-X
I have a question would appreciate any kind of response. Back in high school (1977) I had a 76 YZ125, years went by and I always wanted another one just like it...20 years went by not ride Honda and Yamaha 4 stroke but I came across a deal on a 76 YZ125 from the original owner with all manuals and stuff in really decent shape. Bike only needs a couple cosmetics runs great and looks new...even the tank all nice and shiny... no scratches on the engine nothing. Wont take much to restore this to new condition...He (owner) got the bike in 76 rode in high school and then stored for all these years.... once in while start it up, take it down the street, decided to sell it... my questions are 2:

  1. This bike is not like the one I had that I can remember... It has big (soup cans) nitrogen shocks on front, I never seen those before.... the owner's manual says it is a YZ125 -X. I talked to someone and they said that Yamaha 1/2 way through the year came out with the 1976 YZ125X... a more of competition bike. What can you tell me about this???? What were the differences between the 76 YZ and the 76 YZX? Does that make the bike a little rarer?

  2. Since he never replaced top end of anything... I am planning to dismantle carb and clean, replace top end rings and piston, new reeds, change gear oil. Other than that, what else would you recommend I do to make it mechanically top? What should I do?

Thank you very much

The X model was their latest and greatest race bike at that time. The fork design was pretty cutting edge at the time as far as the design and theory. I don't know if anyone back then actually knew how to properly set them up (short of the factory mechanics). I'd love to get my hands on a set to see what kind of results I could come up with. I'm not sure of any other differences. The YZ's had huge reed cages in that era, but they were all the same size for a number of years after that also. So I don't think the motor was much different than the early '76 125. Not a bad bike at all. Those things really ran well for a 125.

MX Tuner

Taming The Savage CR500
I have bought a 93 Honda CR500. I love the bike but am trying to tame it down to make it more versatile. I added a 13 oz flywheel, but it's still a beast, should I swap it for a 15 oz? Also, I have purchased a gnarly pipe, but haven't installed it yet. How much will this help? I was also wondering if anybody made a wide-ration gear set for it or do you have any suggestions to spread out the gears. Also, it seems to blubber a bit down low, would a Boyesen Rad valve help or should I just change to after market reeds? One last question, would it be worthwhile to have it ported to smooth out the hit and if so, can you recommend a reputable service or suggest a way that I can find one? I enjoy reading your column and look forward to your help!

Thanks - David

Another 2 ounces of flywheel weight isn't going to make much difference. The Gnarly pipe isn't going to tame it down any either. Going up one tooth on the front sprocket will spread out the gearing substantially.

Concerning the low RPM blubbering. No reeds will cure that. That is strictly a jetting issue. Going to a leaner pilot jet will help immeasurably. Porting to tame the power will be the biggest single thing you can do to help make the power more manageable. You can stack up two base gaskets, and this will help mellow it out a bit but porting is the best alternative. Eric Gorr is a wizard with those. Go to for more info.

MX Tuner

Help I've Crashed And It Won't Start Up
I have 1997 Honda CR250R that I recently wrecked and haven't ridden in about 3 weeks. When I wrecked it broke off part of the rear subframe and tore the silencer off. I ended up riding the bike back home without the silencer and that is the last time the bike ran. My problem now is I have fixed all the broken pieces but I can't get the bike to start at all. I put a new pro circuit 304 silencer on it and a new spark plug in. When I kick the bike over, seems to kick harder and makes an almost exhaust noise out of the air cleaner. Is this normal? Or could the reeds be bad or something?

Thanks, Jeff

Sounds like the exhaust is plugged. The noise coming out if the intake certainly isn't right. You may have a damaged reed but it would be a coincidence that it occurred with the wreck. You might try to crank it without the silencer just to see if it starts.

MX Tuner

New Top End - No Power
I have a 1991 DS 80 and I just put new piston and rings in it. The bike starts right up with no problem but lacks power so I pull the plug out and it is wet. So I turn the gas off and ride the bike and it runs great the lower it gets on gas until the obvious it runs out. Also, the spark seems to be plenty strong.

The carb has been cleaned and seems to be functioning correct, and is stock. Please help.

Trevor in MI

I know it seems obvious but have you checked the air filter lately? Either that or the float level in the carb may be too high.

MX Tuner


Split Air Filter Damage
MX tuner, I am having problems with a 2000 CR125, the problem started when the bikes air filter had and split in the seam that was missed when cleaning and subsequently sucked in a lot of dust. The dust appeared to have filed down the ring so that I had no compression. I have since completely rebuilt the top end with new piston, ring, and wrist pin and bearing. I flushed the bottom end and checked for play in the rod and case bearings and they appear to be ok. The cylinder was not scored and there is a minimal amount of discoloration on the intake side of the cylinder with no scratches. With only about three to four hours on the bike it appears to have done the same thing the piston looks fine, the cylinder looks fine but the compression ring is showing sings of extreme wear resulting in little to no compression. The piston and ring used were vertex. Other than trying another ring, I am stumped.

Any suggestions would be greatly appreciated.

Thanks Aaron - St. Johnsbury VT

Vertex pistons are intended to be changed at a very short interval. I think I'd go back with either a Wiseco or a Honda piston and rings. Obviously, check for the air filter to be torn again or not sealing correctly. Check the intake boot between the filter and the carb for signs of dirt. It should be 100% clean. While you have the top end apart, I'd measure the bore to make sure it isn't too large. Excessive clearance can accelerate wear substantially.

MX Tuner

Cold Kick
I have '97 KTM 250 EXC. I recently rebuilt the motor due to connecting rod/crank bearing failure. The bike before I laid hands on it used to be a one kick cold and half to one kick warm starter. Now it takes one kick but it has to be a mighty one, usually with me standing on something as if I need more engine RPMs to get it going. It bump starts easier than it used to and runs great. All settings are the same as before the rebuild with the exception of two things. I added an FMF gnarly pipe (old one was a fatty), and dropped the needle clip from the #4 pos, to #3. The other thing was I didn't have any distilled water for the coolant. But I did have a whole bottle of water wetter, which I poured in. and some antifreeze. My question is, is it possible that the engine is too cool?

Thanks for reading this. Dave Z.


Believe it or not, a "one kick cold" starting bike is jetted too rich on the low speed circuits. If you can get it to start on one kick, I don't think I'd complain, or take any actions to cure it. The difference in compression from the old motor to the new can cause the difference you have. Your motor is not running too cool due to the water wetter and anti-freeze. Even if it were, it wouldn't affect the starting. You can use tap water without doing any damage to your motor. It will run cooler with a 50/50 mix of coolant and water than it will with straight coolant.

MX Tuner

A friend of mine has a 2000 Yamaha YZ250 he would like to find out what the 2 stroke carb jetting setting would be at 600 to 1000 ft. sea-level temps between 70 and 80 degrees low speeds (RPMs) 175 stock main #3 clip (needle). Any help would be appreciated.

There are too many variables to give you exact jet numbers for his bike. The altitude and temp helps but the humidity even has a substantial effect. I don't keep specific jet numbers. Your best bet (or his) would be to jet for your specific conditions. Find a good jetting guide and use it. Eric Gorr has a good one on his site. Go to for the guide. Chances are he'll end up going leaner with the pilot jet to clean up the low speed jetting. The main jet doesn't come into play until about ? throttle openings and up.

MX Tuner

What Bike?
I was wondering what a good bike for me would be. I am 5'11, 190 lbs, and have experience on a 1985 Honda CR125. I was looking at an early 90's Honda XR250. It's just that I loved the power and fun of a two stroke. What other early 90's bikes for under $3000(Canadian) would be a good choice? Preferably 4-stroke. Also out of curiosity is there a real big difference in a 125 2 stroke and a 250 2-stroke?

Tyler - Ontario, Canada.

A lot depends on what type of riding you plan on doing. If you are going to be riding trails and woods mostly, a bike designed for that will be your best bet. Whether it is a two stroke or a four stroke is entirely up to your preference. You can get a good two stroke 250 woods bike and it should have a very good useable power output. An XR 250 is a more than adequate woods bike but isn't quite as fast as a KTM 250 EXC. A two stroke 250 will have substantially more horsepower than a 250 four stroke. An XR 400 is a popular bike but is somewhat limited by its weight and suspension. Any of the Japanese 250 motocross bikes can be made to work well in the woods also. If you look at KTMs, I'd stick with a '95 or newer. The suspension made a good improvement in '95 and the motors are relatively durable. At 190 lbs, you could ride a 125 but a 250 would suit you better.

MX Tuner


Jetting For The Sierras
Hello, thank you for this valuable service! I have 1997 Honda XR650L, totally stock. I plan to do some trips to the Sierra[s], taking trails at 8,000 foot elevations. What changes will I need to make to the carburetion? I realize that other changes may also be needed.


You'll need to lean the jetting to compensate for the altitude. The best thing to do is call a Honda dealer in the area you'll be riding and ask what jetting they normally run in the area. They can give you the most accurate info for riding at those altitudes. You can also check some of the discussion boards that are somewhat specific to your bike. Thumper Talk has some good info. Go to and visit the XR 650 forum. Someone there may be able to give you good info.

MX Tuner

I am looking for big bore kit for 125cc MX bikes

A 2mm or a 4mm overbore have proven to be fairly reliable. Anything bigger than that can vibrate a lot and be less durable than a stock motor. Check with Eric Gorr for the rundown on what your options are. Go to for the lowdown.

MX Tuner

Shiftless XR
Hi there, thanks in advance for taking the time to read this.

The Problem:
I just bought a 1982 (on the frame) XR250R (on the seat) or XR 250. The shifting was awful not shifting at all most of the time. Upon further inspection, I found that the shifter shaft moves in and out (towards the engine and away from the engine) about 1/3 of an inch. When the shifter is out it doesn't shift at all, but if it's in first gear then it shifts only to neutral and not to 2nd or even back to first. If the shaft is in (towards the engine) than it's shifts flawlessly but is extremely hard to get to go into neutral. I can continue to ride by pushing my foot in towards the engine and shifting or maybe putting a bunji cord around the shifter and hooking it to the skid plate but I would like to fix it instead. I'm sure you can understand that. This is my 2nd bike, I can work on cars and now want to work on this bike (never worked on the first). What is the problem? Do I have to crack the case? Or is it a simple retaining clip somewhere. Or is it supposed to shift like this.

Thanks -------Jeremy

No, it most certainly isn't supposed to shift like that. The in and out play of the shifter is not normal. The shifter is only engaging with the shift drum mechanism when it is pushed in. Some shifters have a white nylon piece that helps hold it in place. If this piece is missing or damaged, it can give the exact symptoms you have. You need to get a shop manual. This should give you all the necessary info you need to inspect the business end of the shifter shaft.

MX Tuner

Engine Cuts Out
I have a 91 RM 125 that I can't get to run smooth at 3/4--wide open throttle range. When I'm riding in the powerband the bike revs up and then cuts out repeatedly, it's as if the bike just shuts off and catches itself before it stalls. At lower RPM ranges the bike runs fine. I had a 310 main jet and tried a 330(stock) and a 340 and the problem still exists. Am I making the right adjustments?

It may not be a jetting issue. You may have an ignition problem, especially with a 10-year-old bike. I'd look very closely at the coil wire and the plug cap. You can buy an aftermarket wire and cap for a relatively cheap price (cheaper than a new coil and wire assembly from Suzuki). Also, make sure the ignition components are grounded properly. The coil can develop corrosion under its mounting tabs and give some unusual symptoms.

MX Tuner

Klicking KX
I just bought a 1997 Kawasaki KX250, and don't have much experience with 2 strokes. My bike makes this clicking sound when it's idling, I think its something in the power valve. I took off the pipe and you can push the valve up and down a little bit, it doesn't seem like it should do that. I don't think it's a bearing going out or anything, because it just got a complete top end rebuild last spring. What do you think it is and what can I do?

There is normally some play in the power valve assembly, especially with the KXs. There are a lot of pieces in the KX valve and there is play between each piece. A routine top end may not address this amount of normal play. There are aluminum teeth that can wear and cause an abnormal amount of play. These parts need to be replaced before the teeth wear down enough to break off completely. But this normally doesn't give a "clicking" sound.

Does the sound come and go when you pull in the clutch lever? Some play in the primary drive gears can make some noise.

MX Tuner

Stuck In Third Gear
I have a 1998 RM 250. I was riding it and the shift lever was getting stuck in 3rd gear. Sometimes I would have to downshift to shift back up to 4th. (The clutch was redone a couple of months ago) After riding it I changed the transmission oil. I took it out the following week and it continued to have the same problem. Only this time sometimes when I would start out in 1st gear it would pop out of 1st and go into neutral.

I've seen some RM 250s that have a burr on a part of the shift drum mechanism. This burr can prevent the shift drum to rotate fully and engage the selected gear completely. Right at the end of the shift drum, there is a pin about 8mm in diameter on which the shifter linkage rotates. This pin can get a burr or trash between it and the piece that turns on it. This needs to be cleaned or removed before normal shifting can occur. This can be done by removing the right side cover and the clutch assembly with the motor in the bike.

MX Tuner

Fuel Leak
I have a 1983 YAMAHA YZ250. The problem is I keep on getting a lot of gas leaking into my exhaust pipe and thus not allowing me to get the bike to turn over. I continue to have to remove my exhaust pipe and dump the gas. My float in the carb seems to be working ok, and I have fully clean the entire carb. Throttle is ok. Carb is mounted securely without any noticeable leaks. Can you help me?

A float needle and seat may appear to work normally but still let some fuel leak through over a period of time. First of all, make sure you're turning the fuel off at the petcock when shutting off your bike for any length of time. Even with the petcock shut off, it still may be seeping some fuel into the carb. You should be able to pull the fuel line and check for any seepage. You may end up having to replace the petcock and the float needle and seat to cure your problem.

MX Tuner


Pinch Bolts, Fork Oil, Loc-Tite, & Factory Mechanics
Due to all of the great information you've shared in answers to past questions, (mine and others) I've thought of a few more things that I just gotta know. My bike is a 01 CR250. I recently bought an Applied top and bottom triple clamp kit. The bottom clamp has a three bolt design compared to the stock two bolt. What would be the correct torque for the three pinch bolts? What is the story on fork oil? I've heard that there are only two or three manufacturers and that some 5 weights are the same as other brands 10 weights. Which brands do you recommend? Can you settle the score on where you should and should not use thread locking compound and anti-seize compound? Lastly, can you please tell me what qualifications these so called "factory mechanics" have? I just finished reading another how-to article with incredible advice. This mechanic was explaining how to tighten the steering stem top nut and advised the reader to use channel lock pliers instead of a hammer and punch so as not to damage the nut! WHAT? Please tell me that the people working on the epitome of motorcycle machinery are not a bunch of Stone Age hacks dressed up in factory team clothes.

Suspension fluids are measured in a couple different methods. One manufacturers 5wt oil may not be close to another's 5wt oil. The most accurate scale is the one that lists oils in a fraction. Spectro lists an 85/150 and a 125/150. This is much more accurate of an indicator of actual viscosity than the 5wt, 7.5wt, 10wt, etc scale. Personally, I've had excellent results with the Bel-Ray HV1 fluids. I know their 5wt oil isn't as thick as some others. I know its characteristics and will continue to use it until I have good reason to change. Personally, I stay away from high priced synthetic fluids. Their big marketing ploy is that the synthetic fluid lasts longer before breaking down at a molecular level. You should change the fluid long before that occurs due to contamination anyways.

Loc-Tite is used in places where a fastener isn't frequently removed, like an air box or other body plastic fastener. Anti-seize is used in places where a bolt is frequently moved, like a chain adjuster bolt. Anti-seize can also be used in places where dissimilar metals electrolysis occurs, such as a cylinder locating dowel pin.

Concerning a factory mechanics credentials or qualifications. That varies from one mechanic to another. Getting a job as a factory wrench can be as much political as much as anything else as long as you're relatively qualified. It's the old being in the right place at the right time thing. Personally, I use Channellocks rather than a chisel or punch to adjust the steering stem nut. You shouldn't have to re-adjust it between re-greasing the bearings. So, I adjust it when I'm reassembling everything the first time. I do use a punch for the shock spring preload adjuster locknut. You'll find advice that you find unusual from a lot of sources. Keep an open mind and try to find out why someone does something one way rather than another. I continually hear of different ways of doing things. If it is better in some way, I may start doing it that way. Just because they call themselves a "factory mechanic" doesn't mean it is the way you should do it.

MX Tuner

10 KTM Kwestions
Just picked up a 96 KTM 300 M/XC (with E/XC lights, etc installed).

  1. The manual says the gas/oil ratio should be "40-50:1" -- I am mixing 40:1 using Maxim synthetic blend. Sound okay?
  2. The manual says the gearbox should be filled with "30W Engine Oil." The local dealer recommends an 85W "Transmission oil." What gives?
  3. It has an FMF Gold pipe and "silencer." It is super loud, and it drips oil out of the end-can like mad. If I go back to stock pipe, will I have to re-jet?
  4. The gas tank vent hose is routed into the steering head. Is that okay? The manual shows vent tube running down the frame to the ground.
  5. Running through the gears up the street, the bike just does not feel that fast; Kind of a let-down. Kind of "burp, burp, burp" with no real powerband. Of course, I am used to a sportbike on the street. Is it worth doing a dyno run to see how much power the KTM is making? What should it be making at the rear wheel?
  6. Are full knobbies street legal? I hear not, but they do say "DOT" on them.
  7. The bike's seen some hard use. I want to go over it from end to end mechanically. What are the top 3-5 things to look at and fix if needed?
  8. Any plastic changes between 96 and 98? All the new plastics I find are 98 and up.
  9. The bike is grungy all over. Never cleaned much in its life. Recommend some sort of spray that will dissolve the grunge in hard-to-reach places?
  10. How do I tell how much gas is in the tank? There is no gauge, and the tank is opaque. There must be a way I am missing.


Okay, we'll go down the list?.

  1. Yup, 40:1 would be fine.
  2. There is any number of things you can run in the gearbox. Anything from 85 wt gear oil to Type F automatic transmission fluid. Personally, I'd use whatever makes it shift the best. You'll probably find Mobil 1 synthetic 15w50 will be a very good choice. Whatever you use, changing it frequently will be to your benefit.
  3. The exhaust note is loud because the silencer packing is saturated and the core holes are glazed over. Re-pack the silencer with silencer packing, not household insulation. Be sure the core holes are clear and unobstructed and don't re-pack it too tightly. This will help more than you can imagine. This will also help with the running. You need to re-jet for either pipe, the FMF or the stock. You'll benefit from running a one step hotter plug also. This will help reduce the spooge. Find a good jetting guide and go by it. You'll start out changing the pilot jet first and then go to the needle position and then the main jet last. Try Eric Gorr's website for a good two stroke jetting guide GO to for more info.
  4. The vent tube can go either place. A common misconception is that it can wash the grease off the bearings but the hollow steering stem won't allow anything to get into the bearings (from that source) unless it is cracked.
  5. See #3. Once you get the silencer re-packed, the hotter plug installed and the jetting resolved, you'll be amazed at how much better and cleaner it runs. One other word concerning jetting. The Keihin carb on your bike will work much better the lower you have the idle speed set. Entirely off is the best setting to get some eye opening throttle response.
  6. The difference between DOT approved knobbies and tires that are not DOT approved is the carcass construction. If they are DOT approved, they are street legal. You might need to point the DOT designation out to a police officer.
  7. There is no way of giving you a list of what needs to be done to your bike without riding it and inspecting it. Check everything from chassis bearings (wheel bearings, swing arm bearings, etc, etc) to brake pad and fluid condition to engine condition. Personally, I'd start off by fixing what you know needs repair and go from there.
  8. Nope, I don't think any of the '98 plastic will fit your bike except for maybe the front fender and number plate/headlight.
  9. You need to be careful what you spray on the bike to clean it. You can use a caustic cleaner such as Castrol Super Clean but it will etch all the aluminum parts of the bike. I use Simple Green and am very pleased with the way it cleans. I don't know of anything that works better that isn't harmful.
  10. Get a flashlight to check your fuel level.

MX Tuner



Sticking Throttle
Two months ago I purchased a used 1997 RM-250 and found the throttle to stick every other ride. I've replaced the throttle cable and the problem persists. It has stuck when riding at: wide-open throttle, barely putting, and in the middle. What should I check now?

Make sure the throttle tube is in good condition (not cracked, etc) and that the end of the tube/grip isn't rubbing on the end of the handlebar. I don't use any lube on the end of the handlebar since it can attract dirt. Also check the carb slide for dirt or flaking of the chrome plating. Check the roller at the throttle assembly to make sure the cable isn't getting wedged between it and the housing. Yamaha has a recall on the '96 and newer YZ two strokes for this problem. The RM throttle is very similar and could do the same thing. The only other thing I can think of is if the cable is getting pinched somewhere such as the steering stops.

MX Tuner

Suzuki Carb Oddity.
Hi, I have an '82 DR500, which I picked up a few months ago for $400. It is in excellent condition for its age. The engine seems to produce a very large amount of torquey power. Perfect for mountain trail riding. All I needed to do was re-adjust the valve lash to the proper setting of .004, clean the gummed-up carb, and buy new tires, and the other usual maintenance requirements.

My problem is that the float bowl is out of adjustment, over-flowing fuel. However, the pin to remove the float, which is usually loosely set in, is in this case pressed in. This is very strange. I tried tapping it out, but didn't want to damage it. Is tapping it out the way to go here? Or drilling it out, which of course, would ruin the pin. Thanks for any info.


It may only be able to be pushed/tapped out in one direction. Using a small punch, tap in one direction. If it doesn't go, try the other direction. Obviously be very careful since you don't want to break the cast towers the pin pushed in to. I don't think the adjustment is causing the fuel to overflow. It is probably a faulty float needle and seat.

MX Tuner

Preparation Tips For Winter Riding?
Hello Mark, do you have any tips and/or suggestions for winter riding? I live in Stockholm, Sweden. Winter here means temperatures varying between +5 C to -5 C and changing frequently, sometimes dropping to -15 C or below. Stockholm is at sea level.

I'll do motocrossing, play around a bit in the woods, and go flat-out on frozen lakes.

My bike is a RM 250 '98, stock except Boyesen Pro Series reeds, Ohlins shock. At 158 - 2nd - 42 my jetting is two steps leaner on the main, one step leaner on needle and pilot, as compared to stock. I run a NGK B8ES or equivalent Bosch plug, and standard 13/50 gearing. Castrol TTS or equivalent fully synthetic at 3 % in EURO Green (unleaded) 95 octane with 5 % ethanol (the standard pump gas around here). Trans oil is Castrol "dirtbike trans oil". (It's red, anyway... And a bit expensive.)

This all seems to work fine now at around 10 C. Last winter my RM 125 seemed all right, but you don't learn from not asking... Any suggestions?


The only things you should have to worry about for extreme cold weather is your jetting and possibly the engine not reaching adequate operating temp since there is no thermostat for the cooling system. The colder temps will lean the fuel/air mixture enough that you could do engine damage if you don't compensate for it, especially the main jet. KTMs come with a thermostat for the cooling system. You may be able to adapt one for your Suzuki to help control the engine-operating temp. An engine that isn't at operating temp stands a chance of premature wear at an alarming rate.

MX Tuner

Back In The Saddle Again
I just purchased a used 1998 Honda CR 500. It's all stock. I bought it from a good friend and know that it has been well maintained. I used to race throughout the 70's (The Golden Age, my last dirt bike was a 1977 Maico AW 400 that I purchased brand new) and am stoked to be back in the saddle again.

I will be mostly riding in the Ocotillo Wells area. What modifications if any would be best suited for my new (to me) scoot? I'm 5'9" 170 lbs and used to race Expert/Pro class.

Any help is appreciated!


Your 500 in stock condition will work quite well. Do normal set up like setting the rear spring sag for your weight and clean up the low speed jetting and you should be quite happy with it as it is. You may find the forks to be a bit on the harsh side. In this case, making sure the fork oil is fresh may help a little but you'll probably be much happier getting them revalved by someone like Precision Concepts.

MX Tuner


Planning To Buy - XR200
Hi, I am planning on buying a used XR 200 between the years 2000 and 2001. If u can, could u please provide me some advise about these bikes for a 15 yr old intermediate rider and your overall view of the bike such as things like power and reliability

Thanks, I really appreciate it. Eric

An XR 200 is a great bike for it's intended purpose, and that is an easy to ride trail bike. As long as you don't try to go too fast with it, or try to make it do things it wasn't intended (like jumping), you'll get many years of enjoyment out of an XR 200.

MX Tuner

Blubbers On Bottom
I have a 1990 KX500 Jetted with a Pilot 55, 165 main, 3rd notch, repacked silencer, new air cleaner, new engine seals by a dealer. It blubbers rich from zero throttle to 1/4 then its fine the rest of the way up. Go leaner of the pilot? It's really starting to bug me. Harold.

Absolutely, you'll probably end up at around a 48 pilot. It's amazing what a $5 piece of brass can do for the running quality of a bike.

MX Tuner


Hot Start Switch
I have a Suzuki 1993 DR350S that runs fine and starts with two kicks, hot or cold, unless I stall it on some nasty trail or crash. Then I have to let it cool down about a half hour or find a good hill to get it going. Would a hot start switch help on a CV carb? I don't know of anyone who makes one for this model. If I were to make my own, aren't they basically an air bypass around the carb? Thanks, Wade

You should be able to install a hot start kit for almost any bike on your DR. The kit for a KLX 300 has a fitting that is installed in the intake manifold and would be installed the exact same way on your DR. Yes; the hot start is simply a filtered air leak around the carb that leans the mixture temporarily for easier starting. Check with Thumper Racing.

MX Tuner

Muddled In Midrange
I have 98 YZ 250, which runs great all except one problem. I have a little hesitation at about 1/2 to 3/4 throttle. It clears out fine after that .I also have noticed sort of a detonation sound at idle. Hear are my carb settings and basic set up. All settings are stock except the needle clip has been raised to the # 2 position. Stock jetting goes as follows. Needle n3vf # 3 position, main jet # 172, pilot jet #48 and the air screw is set at 1.75 turns out. I run 92 octane gas mixed with 15 ounces trick octane booster, premix at 42/1 (Yamalube). I run the stock spark plug, which is a NGK B8EG. The plug looks real good, nice tan maybe a little dark


I'm not a big fan of octane booster, especially on a stock motor. It just isn't necessary. The benefit of running a race fuel with a stock motor is the consistency you get with race fuel out of a drum. You may have the idle speed set too high. That can have a substantial effect on low to mid jetting. The pinging you're hearing is dead giveaway. Make sure the slide stop screw isn't raising the slide too much and turn the idle down as far as you can stand it. This is the first place to start.

MX Tuner

I Need A Plug...
I have a 2000 KX 250 with stock jetting and FMF Fatty pipe. My bike likes to wet foul plugs on a regular basis. I have drool on the tail pipe regularly as well. Once I replace the plug, it runs great all day, then next week it will foul 7 times out of 10 right off the bat. It cranks, runs a few minutes then fouls. It is a little dirty down low, but once it revs up, it rocks. I have owned the bike for a year, and have tried minor carb adjustments and plugs to correct the problem. To no avail. I am ready to take action. I just don't know what to change. I take the bike down in December for maintenance, and plan to make my changes then. Could you offer any insight to my problem, and possible fix? Thanks.

Signed, "I need a plug"..... : )


Two things will help. One is running a BR7ES spark plug. The other is leaning the low speed jetting. The pilot circuit is mainly the culprit when you get plug-fouling spooge like you're experiencing. I'd repack the silencer before beginning any rejetting. Make sure the core holes are clear and unobstructed and don't' pack the new packing too tightly.

MX Tuner

High Speed Miss - RM 80
My son has a 1998 RM80 Suzuki. We just replaced the top end piston rings gaskets with good results. But after a short period of operation, we seem to have a miss at high speeds. we've cleaned the carb and jets put a new spark plug in. And wondering if the power ports might have something to do with it.

Thanks - John.

I'd take a close look at the reed petals. If they aren't sealing adequately, it can give some symptoms similar to what you're having. Also, make sure the silencer packing is fresh. Corrosion around electrical component connections can give some erratic symptoms also. Check the coil mounting tabs for rust or corrosion.

MX Tuner

Cracked Case?
I have a 2000 CR 500 and am in the process of rebuilding the top end. I noticed what appear to be cracks on both case halves. The cracks are near the holes that lead down to the crank bearings. One Honda Mechanic who was too involved in his work to step out of his shop, told me the cracks are just casting flaws. Another mechanic said it was ok if the bike was running OK. The bike has never overheated, and the piston, con rod, and cylinder look fine.


I've never seen a set of cases crack in that area. Not saying it isn't possible, just that I have never seen it. I've seen what appear to be cracks that really are casting flaws. If there were cracks, your 500 would be shaking itself apart in very short order. Since you have no symptoms, I'd reassemble it and not worry about it until some problem appears.

MX Tuner


Crusty KLX...
I have a 95 KLX650C that is a bear to start. Although it has electric start its never consistently able to start one the "button". A quick push and the engine will fire. However, it will only run on Non-resistor plugs (D8EA). I given the engine a once over, added a new air filter, check timing, and recheck the decompressor....all are good.

Is my problem electrical, i.e...stator or should I point my search elsewhere??

Thanks - Dave

The fact that it won't run with the recommended resistor plug leads to an electrical problem. The fact that it won't start with the electric starter leads me to believe you have a voltage drop somewhere. I'd check the source voltage to the ignition system at different points. Check it with the battery power only and then with a battery charger hooked up, or even jumper cables hooked to a car. If you're not getting battery voltage to the ignition components, then you have a voltage drop due to a poor connection of corrosion. Check for corrosion at all electrical connections and ground points. This includes places where components are mounted, such as the coil mounting tabs.

MX Tuner

Smokin' KX
Hello, I have a problem with my 1999 KX250, it produces heavy gray smoke from the exhaust pipe and there is oil evident running down the outside of the pipe. I have been told that it is probably a crank case seal. Is this a difficult job? I have a good mechanical understanding but have never worked on bikes before. I have tried my local Kawasaki dealer for a service manual but they tell me they were only produced up to 98. Could you guide me through this job? I don t want to pull it apart and find springs and gears shooting off everywhere!!

Many Thanks - Phil

I know some of the Kawasakis had to have the cases split to gain access to the crank seals. I'm not sure about your KX. I don't think you have to but I may be wrong. You can remove the right side cover, the clutch assembly and the primary drive gear on the end of the crank. The seal is directly under that gear.

MX Tuner


Grenade Reservoir?
Mark, after going through your March 99' issue "Basic shock maintenance and repair" page, I still don't understand how can a grenade size reservoir can hold up to 150-200 PSI of nitrogen or compressed air pressure? I have a 7-gallon size portable air tank which only can hold up to max 150 PSI only. Just compare the size of 7-gallon tank and the small grenade size shock reservoir. I'm just worry that if I charge 150 PSI into the reservoir and it going to blow me sky high.

Second question, if I just want to replace the shock bumper only, The first step is to release all the nitrogen gas out of the shock, Second, release the clevis end nut, put in the new bumper, screw back the clevis end . Recharge the air set at 150 PSI into the reservoir right?

Thank you, Douglas

The size of the reservoir has nothing to do with the capacity it has to hold pressure. The tank I charge shocks out of is only about twice the size of your portable air tank yet it is charged to 2000 PSI. The thickness of the walls of the container are what determine how much pressure it can hold. The stock shock on some of the Honda XRs hold 285 PSI. As long as the circlips is seated in it's groove correctly, you won't have a thing to worry about.

Replacing the shock bumper only can be done the way you describe. It may be a little difficult to get the locknut off the shock shaft since it can be difficult holding the shaft from turning without damaging it.

MX Tuner

2000 KX 250
Well, here is my story... I bought the bike used and it is in great shape. The bike runs perfect, but one day I jumped on it (after about 4 months) and the suspension was rock hard. I was confused to say the least. Looking everywhere for a problem. But none to be found, so I rode it all day and it eventually softened up again. Is my spring too hard? or does my shock need revalving? I really don't know . It is like the shock hardens up after it sits. I am a short guy that only weighs 150 lbs.

Any suggestions? I am also looking for a way to lower the seat height but I can't find a smaller seat anywhere.

Thanx for your time


Jeff G

The swing arm bearings can get stiff during times of sitting if they are dry. That would be the first thing I'd check. You may consider cutting the existing seat foam with a bread knife. But this will result in a harder seat. You might consider having the suspension lowered. This is the most expensive way to go about it but by far the best way. This involves installing spacers in the forks and shock and using springs that are not only shorter but also the correct rate for your weight. It isn't cheap but would help your riding more than you'd ever imagine. Go to for some info on lowering your bike. Ask for Jeremy and tell him MX Tuner sent you.

MX Tuner

Triple TTRed
Hey, me again... TTR225, boys both have TTR125s... I'm looking for basic information on servicing the bikes and also, 1 of the TTR125's shocks are low on fluid, but I can't seem to find a tool to get the plug/screw out, any ideas?

Also, I haven't gone to Whisenhunt yet, because I'm not sure if my boys can handle seems to give me a straight answer (they are 10 and 12, and all we do is trail ride and small jumps, nothing wicked) anyways, thanks in advance, Jon



Your owners manual should give most of the info you need. If not, Yamaha offers a shop manual that will go through the entire bike, from one end to the other. This will go over checking and/or servicing the fork oil. This will include any special tools needed.

Whisenhunt is not a difficult area. They show the trail difficulty on a map in the parking area. And if you encounter a trail that becomes too difficult, you can turn around and return the way you came. The central trail is a road large enough for a jeep to drive down. There are some difficult trails but they are marked "most difficult".

MX Tuner


PW80 Woes!!!
1999 Yamaha PW80. Problem: The bike is hard to crank but it will crank. Once it is warm, it will not run unless the choke is in the full position. As soon as you release the choke, the bike quits. Also, the bike's power has been cut tremendously. It does not run properly. Any suggestions? We have tried adjusting the carb. but no luck.

Thanks for your time and help.

Steve - Atlanta, GA

Sounds like you have a plugged passage in the carb. Probably a plugged pilot jet. Try cleaning the carb with some aerosol carb cleaner. Be sure to blow through the passages to verify they are clear.

MX Tuner

Fuel Mixture & Plug?
Hi, I have a 94 Honda CR 125. I am not sure what the fuel mixture is supposed to be. And also what size plug do I run in it?

Thanks - Aaron

If you're running at wide-open RPMs nearly 100% of the time, I'd run a BR9ES. Otherwise, use a BR8ES. Don't bother with the high dollar plugs. They are a waste of money.

By fuel mixture, I'm assuming you mean the fuel/oil mixture. Your CR will do quite nicely run at a ration of 40:1.

MX Tuner

I have two questions:

  1. I have a 1991 Kawasaki KX 80 that needs a head and I found one off a 1986 and I was wondering if it would fit?
  2. My 2001 Honda XR400R I think needs some mods. which brings me to ask what the best mods. are that I can do with out sacraficing reliability?

The head for the '86 KX won't interchange with the '91 head.

The biggest improvement you can do for an XR 400 is to get the suspension fixed. The spring rates are unbalanced from the factory. The fork springs are too soft for anyone over 150 lbs and the shock spring is too stiff for anyone under 210 lbs. Getting the spring rates closer to what you need will help a lot. Race Tech sells a compression adjuster assembly with Gold Valves that increases adjustability, improves plushness and bottoming resistance. The improvements are dramatic. By far the best money you can spend on that bike.

MX Tuner

Jetting Tip?
I need jetting tips for 01 CR 250 pc pipe and silencer---delta 2 reed cage--Maxima Super M at 40-1 VP race fuel o-1500 ft altitude

---thanks in advance

I can't give you exact jet numbers. Your best bet is to rejet according to your local conditions for the best throttle response. Eric Gorr has an excellent jetting guide on his website. Go to for more info. You'll need to go leaner to compensate for the V-Force reed cage. You'll be quite impressed with the motor once you get the jetting sorted. Those reeds are great!

MX Tuner

No Brakes
Hi, my name is Andrea, and I'm writing for my friend who has a question on his recently purchased 1998 Suzuki RM250. He is having a problem with the rear brake and has to use the front one along with downshifting in order to stop the bike. When he looked at the rear brake he noticed the reservoir on top of the brake was half to 3/4 full of dot 4 break fluid. It looked to him like the brake pad wouldn't collapse/pinch. He is trying to troubleshoot what the problem may be, to find a way to fix it on his own. If you have any suggestions please email back with them. It would be greatly appreciated!


Is the rear brake pedal feel soft or stiff? If it is soft, the master cylinder isn't generating proper pressure against the brake rotor. Bleeding the brakes may help eliminate this problem if there is air in the system. If it is stiff, the caliper piston or sliding pins may be binding so the pads aren't applying the pressure against the brake rotor. This will require finding the parts that aren't moving freely and cleaning and lubrication them.

MX Tuner Newsletter
Join our Weekly Newsletter to get the latest off-road news, reviews, events, and alerts!