Technical Questions? Ask MX Tuner

Nov. 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.

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All Forked Up
I own a 96 KTM 360SX, and love it. Everything but the forks.  As an avid rider, I have many tastes and so far the entire bike has preformed very well in all of them.  But I have had an on going problem with the forks.  I have three sets of seals and bushings, along with regularly changing the fluid and cleaning the wipers.  As a Harley Tech. I have little exposure to the ever changing market of MX.  All the local dealers and KTM owners that I have talked to have had similar problems.  Also I have progressed past the stock settings.  I am 6'3" and around 220lbs, and I over tax the suspension.  I have been able to get a heaver spring for the shock and it seams to work wonderfully.  I heard rumors of machining the forks to accept the internals out of the newer CR forks.  If this is true I have full access to a decent machine shop.  Your help is much appreciated and needed.

The KTM forks work fairly well once dialed in. One update KTM had with their fork seals was to remove the spring inside the seal, unscrew the ends, (one end is tapered and screws into the non-tapered end forming a complete circle) and cut 4mm from the non-tapered end. This tightens the new seal around the fork tube tighter. I've heard of guys doing this to the dust seal spring also.

I'd get springs that are rated for your weight and play with the oil weight and level. Try 20wt oil in the compression leg set at 130mm. Use 10 wt oil in the rebound leg set at the same height. This, combined with stiffer springs should give a ride close enough that you can fine tune it with the clickers.

MX Tuner

My YZ Won't Zing
I have a 1981 YZ-250. My problem is plug fouling and black goo being expelled from the exhaust as well as leaking from the pipe after being shut off. The bike generally starts on the second kick when cold (with the choke on). If it stalls after riding for awhile (which it often does) it can be difficult to start.

I carry extra plugs just in case of fouling. There is also a very pronounced miss during acceleration. When I parked the bike I noticed that fuel was leaking from the overflow line. I have been using castrol 2 stroke in my premix at 40:1 ratio. I suspect that perhaps the float needle is not seating properly or the seat is loose. This could explain the leaking from the overflow tube. Could this also be the cause of the fouling and the black goo? I am going to try a synthetic premix oil as an option. Could there be a possibility of a poor electrical connection or weak CDI unit or coil.

Any help you could offer will be appreciated.

Thanks, Tired of Pushin

I wouldn't try switching oils until you eliminate some other possibilities. First of all, fix the carb issue. If it's dumping fuel out the overflow hoses, the float isn't working properly for one reason or another. Either the needle isn't seating properly or the level is set wrong.

Once you get that straightened out, repack the silencer. The packing will be saturated and may be blown out anyways. Make sure the core holes are clear and unobstructed. Don't pack the silencer too tightly. The packing has to absorb pressure pulses to work correctly.

Unless you're running at wide open RPMs 95% of the time, you can benefit from running a spark plug one heat range hotter than stock. Run a BR8ES plug. This should help reduce the spooge coming from the exhaust.

Any corrosion on an electrical component or connector can give some erratic running symptoms. Make sure the ground points are also clean. A chipped reed petal can give some unusual symptoms also. Don't forget to check these basics.

MX Tuner

Shiftless Bayou
2001 Kawasaki Bayou 220, auto transmission, 5 speed with reverse, 2 wheel drive. When shifting from first to second gear, the foot shifter is so tight it doesn't want to go into second gear until after 2 or 3 HARD tries. This happens when going up hill, but more so when going down a hill in first gear and needing to change to second. This has been happening almost since after buying new. Your help would be so greatly appreciated.

Thanks, Emily

Sounds like the auto clutch mechanism isn't releasing fully. This would be the same symptom as a manual clutch not releasing or dragging. I'm not familiar with that particular auto clutch but I'm assuming there is an adjustment somewhere, maybe inside the motor. Sounds like it's time to take it back to the dealer for a minor adjustment.

MX Tuner

I have resently purchased a 1981 cr125r ellisnor. The used bike dealer assures me that there was a new wiseco piston in the machine and had under 30 hours on it . I rode the bike for 4 hours and oil mixture water in the rad levels are all fine but as i pulled up to my trailer i shut off the bike and now it won't kick over.  the bump starting wont even budge the transmission allows gear changing and it seems the piston is seized my question is are there any special proceedures to rebuilding a top end or tips you can provide me with . I have overhauled car engines how would 2 strokes differ??

Two strokes are similar from the standpoint they have a piston, rings and connecting rod. The similarities end there, though. Two strokes have a slew of differences from the intake system to the exhaust system. Getting a good manual will be invaluable and the first step in this learning process you're attempting. It isn't rocket science but there are steps that should not be overlooked. A good manual (try ordering the Honda manual from the Honda dealer) should give all the info you require.

MX Tuner

XR650L Compression
Dear Mr. Klein, I own a 1994 Honda XR650L, which I have modified quite a bit:

Among others, the engine has just been rebuilt using a 101mm 10,5:1 JE forged piston, and a White Brothers 1652 all around camshaft. The cylinder head has been treated for better gas flow. The feeding is taken care of by a flatslide 41mm Keihin FCR carb with an accelerator pump breathing through a K&N filter. Exhaust gases leave through an XR's Only oversized set of headers mated to an Arrow tailpiece. I am currently in the process of running it in. I ride it at slow speeds and varying, low rpms (2-3000rpms, using my ear; my ear hasn't failed me in the last 12 years I've been riding motorcycles).

The problem I am having is that the engine occasionally pings (self-detonates) at the rpm range I rev it (2-3000rpm). And this isn't because I have it in the wrong (high) gear.

I have tried using the "super"-98 octane unleaded we have here in Greece. This eliminates the detonation in all occasions except when I open the throttle very suddenly. In this case, it pings for a fraction of a second and then in clears. Can it be that the compression is too high?

All associated literature claims that the piston and camshaft combination I am using is a very popular and safe mod. Are they wrong?

Is it that I may be using bad quality fuel? I'm buying gas from well-established firms such as BP, Shell etc. I use the bike for my everyday transport as well as racing (enduro and supermotard) and I want to avoid using aviation/racing fuel or fuel additives.

Any advice? I thank you for your time and help

Best regards, Manos/Greece

I'm not familiar with the quality of fuel you have in Europe. It is entirely possible that the ping is due to a lean fuel/air mixture in the lower circuits in the carb. Try richening the mixture with either the low speed fuel screw (this screw is very sensitive to adjustments-1/4 turn is a substantial change) or with a richer pilot jet. Even if the carb was jetted fo your individual application, the list of mods you give is fairly intense. It can be hard to anticipate your jetting needs.

The other possibility is you need higher-octane fuel than you can buy at the gas station. You may be able to get by with adding a little octane booster when you fill up the tank.

MX Tuner

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Performance Mods - YZ250F
Hi-there... Your website it?s beeing seen in Portugal! Congratulations!

I Race in one YZ250F 2001 and I Would like to know if you have any recomendation to improve my bike (If it?s Possible).

Thanks in advance,


I've built a couple big bore motors with the 250F. Going to a 2mm bigger piston helps immeasurably. This requires having the cylinder bored and replated. Wiseco makes a piston and Cometic makes the oversized gasket kit. Compression is raised to 13.5:1 so you'll have to run race fuel. The big bore motor has a BIG improvement in midrange and top end power over the stock motor. I've heard nothing but good things about the Dr.D pipe for the 250F. The stock exhaust is a bit restrictive at higher rpms.

The suspension can be fine tuned to your weight and riding style. This can be done with different spring rates, fork oil height, and a number of other adjustments. Your owners manual will cover a lot of these fairly thoroughly. Getting the suspension revalved for your weight and skill level will help quite a bit.

Tire choice is a critical area for performance. I know way too many guys who choose a tire that isn't for the terrain they are riding on and suffer the poor results because of it. Good tires are well worth the expense.

MX Tuner

KX Kakked
I have a 2000 KX250 I bought a couple of months ago.  The bike has run perfectly until now.  A couple of weeks ago I did about 80 miles of trail riding on it and it ran perfect.  A few days ago I brought it to the track and the bike started up fine but when I took off on it I noticed it had very little power and then a few seconds later it killed.  I pulled the spark plug out and it was a little wet, so I poped another plug in.  It started up again and ran for about 5 seconds and killed again and wouldn't restart.  I took the plug out and it didn't look very wet, so I wiped it off and put it back in and it did the same thing as before.  The bike has an aftermarket pipe and aftermarket reed valve on it.  The previous owner jetted the bike to run with these modifications, and it ran great, but it was a little on the rich side.  I pulled the carburetor off and the insides were clean, and I saw no point in changing the jetting since it worked fine before.  I also pulled the silencer off and checked the packing. It was in pretty bad shape so I replaced it but this didn't help.  The piston and rings have about 20 hours on them, and I'm running a premium synthetic oil at 32:1 with the stock spark plug.  Any suggestions on what to check next.

Thanks, Michael
Baton Rouge, LA.

My next step would be to inspect the reeds. Some of the aftermarket reeds are made of carbon fiber. Some of these carbon reeds have a relatively short life span. The reed petals can chip or fray. If this is happening, it can give the exact symptoms you are having.

Either that or you may have a problem with the carb. A thorough cleaning (this means all the passages in the carb body and all the jets) might be in order.

MX Tuner

Dragging Clutch
I have 1996 Suzuki RM 125 with a dragging clutch.  I had local dealer install new clutch plates. Complete with fibers, steels and new springs.  The clutch still drags. I have adjusted it with little or no free play and it still drags. The local dealer disassembled and reassembled it 3 times. They even called Suzuki factory support technician. We still have not been able to figure out the problem. Would appreciate any information you could give us.

Thanks, Vern

I've run into this before on the mid 90's RM 125s. I got a significant improvement by adding a shim under the release bearing under the pressure plate. One other possibility I thought of since (and haven't had the chance to try yet) is the clutch springs are coil binding. In other words, the clutch plate can't move fully because the springs are compressed to the point the coils are touching each other. Adding a flat washer under each spring screw can add to the total height of each spring screw casting. The outer diameter of the washers has to be smaller than the inner diameter of the springs. This will release some of the spring tension on the springs but will also allow the pressure plate to move farther from the clutch hub, reducing the amount of drag.

Like I said, this is something I thought of but have not had the opportunity to try. If you try this and it helps, please let me know.

MX Tuner

Jetting With PC Pipe
Hello, I have a 01 yz 250 stock accept for a pc spark arrestor. Stock pipe. After I put on the spark arrestor I have black goo coming out the pipe. Pro circuit said to jet at 175 main, 2nd clip on the needle and a 45 pilot. I still have black goo coming out. Any suggestions? The bike runs great though. I run 92 gas with Maxima super m at 32 to 1. I there a better oil and ratio?

Thanks, Mark

First of all, don't trust PC's jetting recommendations. Your local conditions can vary too much. A 175 main sounds too rich. The Super M is a great oil lubrication-wise. But it is a very dirty burning oil. I'd stick with a proven oil like Yamalube 2R or Honda HP2. Both are synthetic blends and are among the best oils available.

Let's see... spark arrestor. So you're riding it in the woods.  There is no way you can run the bike hard enough to use the stock plug. You need to go at least one step hotter. I'd use a BR7ES. This will cut down on the spooge significantly.

MX Tuner

Black Goo
Hi. I have a 2001 KX 125 that I bought brand new back in early October 2000. When I first got the bike, I was running the recommended 32:1 gas and oil mixture. I had a problem fouling plugs after about an hour of riding time. I bumped the mixture up to 40:1 (Leaner on the oil side, but richer on the gas side) using Castor 927. That took care of the problem as far as the plugs go. But I am still blowing a  black sticky residue (which I assume is oil) out of the silencer. This is very annoying especially when its all over the swingarm, and rear caliper. The bike is bone stock, and doesn't have many hours on it at all. The problem isn't as bad as it was when I was running 32:1, but its still a problem in my book! I was going to try and maybe drop the clip position on the needle 1 clip size; I have been told that it will help, but I figured I would check with you guys first. Any info you can give me will be greatly appreciated. Thanks!!


You're on the right track. You definitely need to lean the jetting. Start with the pilot jet, though, not the needle position. Try Eric Gorrs website for a good jetting guide. Go to for more info on that.

The 927 is a castor based oil. Very good for lubrication but bad for oily residue. If there weren't any good lubricating oils available, I'd recommend it but there are way too many good choices to need to put up with the residue.

MX Tuner

I have a 2001 CR125R and I have problems starting when the engine is cold.

  • I just rebuilt the top end, I replaced the cylinder rings and gaskets. The cylinder look like it was in good condition, physically. I replaced the ring because it looked like I was getting blow-by. There was a normal amount of carbon build up on the piston top. This cleaned right up using a little two stroke boat decarbonizer.
  • The stock reeds look like carbon fiber. They look fine. There is no gap between the cage and the reed.
  • The carb is clean, I have the stock #380 jet installed.
  • I am using a new plug that produces spark when touched to the outside of the cylinder.

The only way I have been able to start it when cold is to use starting fluid shot past the air filter.  Once the engine has warmed it starts fine, first kick. Then engine runs fine, plenty of power.

Do you have any suggestions as to what I can test next?

Thank you for your time!!!

Sounds like the choke circuit in the carb isn't working correctly.  Either that or the float level is set too low. I'd go through the carb and look closely at all the adjustments. Check both sides of the float when you check the float level. I've seen one side check fine and the other be off significantly, all this from the factory.

MX Tuner

XR or KLX - That Is The Question?
Hi, I am torn apart by these two bikes.  The XR has a name and I want it.  However the KLX is more updated (liquid cooling,etc.).  I don't know which one to choose.  I am looking at the 250cc model for both of them early 90's I hope.  My question is:what should I look out for whne buying an early 90's model of one of these.  What were some common problems of these bikes.  I am going to be doing mostly trail riding and a little MX.  What are some cheap mods I could do to beef both bikes up a bit.  And I have read many letters of yours and understand that the XR is not a MX bike, but hey there have got to be some good mods out there.  Thanks a whole lot for your time.


Neither one is a bike made for motocross. A good friend of mine broke a KLX in half riding it on a motocross track. That isn't saying the KLX isn't a durable bike. The KLX is an excellent bike but it just isn't made for motocross. Neither is the XR. Neither one has suspension suited for jumping at all. Both can be modified but the results are marginal. Thumper Racing makes a slew of hop up parts for the XR and the KLX but all that comes at a price. Four stroke motor mods are generally much more expensive than a two stroke.

Both bikes have their shortcomings but those are small in comparison to making sure the bike you're looking at is in good condition mechanically. That can be far more costly rather than a few relatively small problems both bikes have.

MX Tuner

YZ 125, Yamaha 1996
I bought my dirt bike used so i dont know what is up with the top end. I scraped it a little bit so I brought it to a yamaha dealer. I thought that  all I had to do was bore it out and get a new piston and that was all. But  instead he said i couldnt bore out my tope end because it was nickel plated.  I was just wonder if it was the stock material or nickel plated would it be  able to be bored out? I already sent it in but was wondering if it was the  wrong thing to do if it was able to just get bored and adn get a new piston.  I would have saved a lot of money. I know for sure that I did not have a  sleeve because it was all one piece so it was either the stock material or  nickel plated like he said. thank you for your help.


Your YZ has a plated cylinder from the factory. If it gets damaged, you can have it replated the stock piston size. You can also bore the cylinder and have it replated to the larger size. Going 2mm bigger would result in a significant increase in power over the entire rev range. This is a common mod used in race bikes. Some people recommend a steel sleeve but I just haven't seen any benefits of doing that. It is more costly and needs to be bored later in life when a plated cylinder won't unless some damage occurs.

MX Tuner


Honda - Baja 250 (aka Super XR250)
Hi Mark - I've got this steering wobbling problem whenever I travel on/off-road at high speed. But the problem reduce whenever I carry pillion or let go one hand (on road). However, I've tried lowering my rear height and even softening the rear suspension which of course affects the race sag but still in vain. Hope you could advise on this. Thanks!

KT - 21.09.2001

I wonder if your fork springs are too soft. This would contribute to the symptoms you're describing. You may be able to use preload spacers to help reduce the front dropping too much. But this would be an attempt at curing the symptom instead of the problem. Stiffer springs would most likely be the correct way to fix this.

MX Tuner

CR500 Parts Swapping...
Mark, first of all let me say what a great column you have and how much I appreciate the fact that someone like you would share your knowledge with such patience. I have a 85 CR500 which has several mods but the ignition is stock and I have a Coil and CDI box off of an 87 CR500, that I know is good, can I swap out the Coil and CDI box on the 85 with the 87?  I know that the Coil mounts differently but I think I can over come that.  My main concern is that the bike runs great up to high RPM and then it's starts to break up (my guess is the CDI or Coil).  I know that high RPM is a nebulas statement and most of my friends who ride the bike never notice it because they never push it that hard.  I have a freshly packed silencer and  a "works" pipe, jetted the pilot and main, changed the clip position and turned the choke idle screw all the way in and the bike is crisp and only loads up after 30 min or so in tight woods (I'm a little afraid to jet it down anymore and I run a 14oz flywheel weight) it will clear right out after about 1/2 mile on a straight  away.  I run Yamalube 2R at 32:1 with Amoco 92 octane fuel and am thinking about changing the pipe to a FMF or Dyno Port?

Thanks for taking the time to read this....

Highest Regards, Andy

The deciding factor for the ignition swap would be the connector where the stator plugs into the CDI harness. If they plug together, you'll be okay. I'd be a bit surprised if they didn't, giving the somewhat subdued nature of open class development over the years.

Make sure the reeds are in good condition. You still may be a bit rich across the board with the jetting. A crisp running 500 should be able to run in the woods continually and never load up. You might consider a spark plug one step hotter.

MX Tuner

Beer or XR200?
I recently purchased a 1984 xr200..the price a 30-pack of beer.  The bike ran when I bought it but was in dire need of a new head gasket.  I am having that repaired but am interested in finding out if this bike is worth dumping any money into.  I know that 1984 was one of the years that honda had produced this bike with dual carbs......I'm just not sure if this is a good thing or a bad thing.  I would greatly appreciate if you were able to send me some info on the type of bike that I bought and if it was worth the 30-pack of beer.  Thank you in advance!!!


The dual carb XR wasn't a bad thing, just difficult to get right if someone screwed with the linkage adjustment between the carbs. They weren't supposed to open at the exact same time. Actually, it was a pretty good bike. Just don't expect too much out of it since it is, after all, 18 years old.

You ask if it is worth dumping any money in to. It depends on how much you have to dump into it, how much work it needs.

MX Tuner

Suspension Dial In
I just bought a 2002 honda cr250.  i weigh 135.

i am unsure as to where i should set my suspension at.  i mainly ride at my home.  it is a supercross-style track.  doubles, flat landing jumps, whoops,  and bumpy straight a ways.  i have about ten hours on the bike. i change the fork compression about 7-8 clicks softer than stock; the fork  rebound is about 5 clicks softer than stock;  the rear shock high speed is  about 1/2 turn softer than stock;  the low speed is about 7-8 clicks softer  than stock.  and the rebound is 6-7 clicks softer than stock; and the spring  is at stock setting.  my back is still hurting, but not as bad as the first  ride.  on a flat landing, or sloped with front and rear hitting at the same  time, the bike kicks up a bit; enough to jump my feet off the pegs. I was also wondering about what oil i should use?  we have used Pennzoil for  the past few years on 98 cr125's.  my dad has this thing about new bikes and  using hp2 oil @ $6 a pint.  i also heard that valvoline make a two-stroke  oil now.

You need to go on a triple cheeseburger diet. Backing out on the compression adjusters is a good step in the right direction but I wouldn't back out on the rebound. They need to be close to the stock settings to prevent bad things from happening. You really need softer springs, front and rear. At least set the rear spring sag for your weight, or as close as you can get it.

Your owners manual goes into detail about how to set that. Do one slight variation, though. When they say to take a measurement with you sitting on the bike, do it standing on the pegs instead of sitting down. This will eliminate a big variable of where you sit on the seat. Plus, you never sit in the same place when you're on the track anyways. Once you get the spring softened, it should give a more compliant ride. Put the rebound clickers back to the stock setting and adjust the compression clickers to your preference.

Personally, I have to side with your dad on the Honda HP2 oil. That is one of the best oils around at any price.

MX Tuner

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It's a Gusher!
Hi, i have a 1994 RM 80, it has a racing carb and every time i switch the fuel on it gushes out of the overflow pipe at the bottom and right hand side of the carburettor. ive had the carb in bits and clean it out not just before this problem occured do you think i damaged something while doing this? any help would be brilliant! thanks a lot! p.s great website.


The float needle isn't shutting off the fuel flow properly. It may be that the floats are installed incorrectly. Even if the carb is assembled right, the float needle and seat may need replacing to get the fuel flow to stop.

MX Tuner

Seized RM - Broken Ankle
My son rides a 2000 rm-125.We found one in new cond. and,after riding,decided it was jetted too rich (smoked alot,black plug).It had the stock main jet(175) so I went to a 170.He rode the next day and said it ran better.I checked the plug and it was still black.The following day,while skimming thru whoops ,the damn thing seized and spit him off.He ended up with a broken ankle.

We used gas from the same jug as the day before.This bike has maybe 15 hrs on it.I can't understand how this happened.Any thoughts are appreciated.


The seizure may or may not be related to your rejetting. When rejetting a carb, it is necessary to start with the lower speed circuits first and move your way up the throttle opening scale. In other words, start with the pilot jet/air screw setting. Once you have that leaned out sufficiently, move to the needle position. Then go to the main jet. You could put a 120 main jet in and it won't help a rich condition on the pilot circuit.

MX Tuner

Y C YZ Leakage
I recently bought a 86 YZ125 off a friend of mine knowing that the top-end was most likely ready to go. It was still running but no compression to speak of. In to the shop, new piston rings and a 1x-over on a cylinder that I was suprised to see that was still at stock piston size. I just got it back yesterday when we start it up ojn its virgin run. Seeing an excess amount of casing oil coming out the overflow we think the shop guy filled it a little heavy, so we kill it then kick it over again, bingo no more oil. Bringing it home I kick it over again and damned if its not intermittenly spittin out up to 1-oz of oil. Im thinking the shop guy bombed, and maybe the rings arnt sittin right, getting blow-bye in the top end, also oil is coming out the tail pipe. other then that the bike is a beast at top end and sounds great.

The gearbox and the crankcase are two separate sections that should not be affected by each other. The crankcase has the fuel/air mixture flowing around the crankshaft and going up through the transfer ports in the cylinder to the combustion chamber on top of the piston. There is an oil seal at each end of the crankshaft. The left seal prevents air from entering, which can create a lean running condition. The right side seal prevents gear oil from entering, which can create an excessive amount of spooge from the silencer and also oil foul spark plugs, not to mention make a lot of white smoke from the exhaust.

The oil drooling from the transmission overflow hose is most likely due to an overfull transmission. Chances are the top end work is unrelated.

MX Tuner

Noisy CR
I own a 1988 Honda cr 125.  This is my first two stroke bike.  It was in very nice condition when I bought it, the bike was in storage for a three years without being started.  I have been riding it on and off for about 2 years.  I have been gearing and tuning it up for mountain trail rides.  This year I have noticed it makes engine noises louder then the newer bikes.  Noise really only is heard when idling.  It sounds like gear lash or something like a skate board going down the street!  I have change the clutch plates with steel. Also I had found that the water pump had corroded through the case.  I had to use JB weld to repair the hole and replaced the impeller.   I had the top end rebuilt with using a wisco piston.  I was wondering what am I hearing and what is the acceptable noise level for that year of bike.  I have change the transmission oil often to review any metal in the oil.  So far,  no major signs in the oil, just the black gray color. The bike really has not been rode alot but stored most of its life.  Could it have a bearing starting to go out in the case due to the long storage?


It is relatively common for some noise to come from the clutch area. As the clutch basket bearings and races wear, they can get loose enough to generate noise. I doubt if it has anything to do with sitting for a long time, since a lot of newer bikes make a similar noise fairly soon.

MX Tuner

Low Compression
I have a 2001 xr250r that seems to have lost compression. I removed the head and jug and checked the rings and cylinder. both aren't showing excessive signs of ware. when I replaced everything IM not sure that I got the timing correct. but if I didn't get I correct I still don't think I have allot of compression. ive even tried kicking it with the decompression cable disconnected. please help. also is there a company that makes a repair manual for such a new bike. thank you for your time,


You may have made the same mistake I have made before. Under the cam, there is a spring-loaded pin that engages with the auto compression mechanism on the cam. This pin has to be in place for the auto comp release to work properly. On the motor I built, the pin had fallen out when I had it upside down and I didn't catch it. You should be able to see this pin through the right side intake-valve adjuster-cap without having to remove the entire head cover.

I'd order a manual from Honda.

MX Tuner

All Wet...
Please help!  I just got a new 2002 kx 125 kawasaki. (4days old)  The dealer put some gas in it at the store with the oil mixture on the rich side. I understand why. This is for the breakin period. It ran alright for a little while, then it started to foul the plugs. I expected this. But now we that we put in the proper 32:1 gas mix (kawasaki 2 cycle oil) we cannot get the thing running without taking the plug out and drying it out. When it starts it will only run for 10 seconds and dies. I remove the plug and it is wet. Have good spark. Is this oil any good, it looks nasty to me.  Thanks!

Aarons dad.

I doubt if the oil is your problem. I don't know anyone who uses Kawasaki oil, but I don't think that's your problem. Sounds like it is running way too rich. It is most likely too rich jetting-wise but even that shouldn't make it only run for 10 seconds. I'd look closely at the carb and the float level or float operation. Is there any fuel leaking out the carb overflow hoses?

One other possibility is they may have put a different oil in it at the dealer that isn't compatible with the Kawasaki oil. They may have poured from the wrong gas can. The only way to be certain is to drain the fuel tank and carb completely and start with something you're more comfortable with. I'd shy away from castor-based oils. Yamalube 2R is very good oil, as is Golden Spectro or Honda HP2.

MX Tuner

Clutch Action...
I have a 2000 CR 250.  I didn't like the clutch at all when I first bought it. It was far too stiff.  Now it totally sucks.  I have oiled it and adjusted it. Now it doesn't disengage at all. What can I do to get my clutch (1) to work (2) to work so smoothe that I can operate the lever with 1 or 2 fingers.  Wow! Talk about arm pump!

You may have some galling occurring at the end of the clutch pushrod where the actuating arm pushes it. But try a couple other things first. Get a new cable. The stock CR cable from Honda should be fine. If you don't have a pressure cable luber, buy one. They are well worth the $15 investment. Lube the new cable with either WD 40 or Tri-Flow. Don't use anything other than these. Tri-Flow is better since it has Teflon in it. Now get some clean grease (wheel bearing grease is ideal) and lubricate the barrel end of the cable where it goes in the lever. If the cable end has a plastic sheath or a sheet metal end over the lead barrel, get as much grease as possible under there. This HAS to slide as the lever is pulled. Now put a big glob of grease in the hole the cable goes into and also a little in the pivot bolt hole. Greasing these two holes can make a big difference in the effort required to pull the lever.

If this doesn't give the lever pull smoother than a new CR, you may have the galling on the pushrod end. You'll have to remove the clutch pressure plate to remove the rod to inspect it.

MX Tuner

Dragging DT
I have a 1977 Yamaha DT 250. 3800 miles and all stock. My problem is that it won't run smoothly through the rpm range. It seems to really miss at 3000 rpm. It runs okay for a couple of minutes when it's cold then gets worse. It is running rich with a lot of oil coming out of the pipe. I have replaced points and plug, jetted down and up and tried changing the needle positions. Nothing seems to help. I have taken it to local shops but they don't have any luck. Any Ideas? Thanks, Ron

I'd start by replacing the right side crankshaft seal. Sounds like you're motor is sucking the gear oil into the bottom end and burning it.

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Noisy KTM 520
Hi, I have just sold my 2001Honda XR400 and got a new 2002 KTM 520 EXC.

The XR400 had a very smooth sounding engine, but 1st time i started the engine on the KTM I instantly noticed the engine had a very definate rattle to it while it was idling in neutral. The rattle almost completely dissapears when i pull in the clutch lever.

the rattle is also very noticeable when riding at low engine speeds. The dealer i bought the bike from said the noise was completely normal, but i was looking for a second opinion. Do KTM's usually have a  rattly sounding engine?

Any help would be appreciated

Thanks, Alan.

The KTM is a race bike that wasn't designed to be quiet running like your XR was. The noise you describe sounds like a relatively normal clutch noise. Some bikes make it more than others. A clutch has to have a certain amount of movement between components to work. As long as your dealer is aware of the noise, I wouldn't do anything more than keep tabs on it to make certain it doesn't get worse. Keep that oil changed frequently. Big difference in the service intervals between the 520 and your old 400.

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Loosey Goosey Honda CR 500, 1986.
Hi Mark and thanks for the previous help. Well heres my new problem. I just finished rebuilding my 86. I notice that my shifter has about 1" of in and out play. I don't remember it being that loose when I tore it down. I've checked everything ( tore it down again ) and I can't find anything wrong. On the right side cover there is a cast in rib that looks like its supposed to keep the shifter from moving in and out too much. Is this wore down? If so is there an easy fix, like inserting a bolt in the end of the shifter shaft to take up the play? I don't want to fire it up with this much play, it looks like it may tear up new Boyseen ignition cover. Any ideas?


There may be a white nylon collar that goes between the center case and the shifter shaft mechanism. If this collar is missing, the shaft will move in and out abnormally. I can't see the side cover wearing that much. I'd look closely at a parts diagram and see if there isn't a spacer collar gone.

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KX 500 Burbling!
I have 85 KX 500 and it always seems to blow blue smoke.  It starts right up all the time and idles perfect.  But in the mid range it starts to smoke.   When I get into 4th & 5th  it runs really good(mostly wide open).  I have  changed main jets, clip positions, and still will not run right. The bike I  can no longer get parts for (discontinued).  I had the brass arm that shuts  off fuel break and I could not get the part.  I had to find one that fit.  I  found one from another carb and it works.  Also when I rebuilt the motor I  notice that the head was very thin as if someone milled a few times!  The  compression on this bike is amazing!  Could the head be a major factor or the  carb?  Could it only be that the bike is for race gas?  Or it will make it  run richer?

Thanks  DJ

For carb parts, you might be better off getting a new, more modern carburetor from Sudco or Carb Parts Warehouse. Sounds like your pilot jet is too rich. Changing the main jet just isn't going to help lower throttle setting jetting issues. The main jet only begins to come into play over half throttle.

If the head has been milled, you may have to run race fuel. I'd check the compression and compare it with what the manual recommends. If it is too high, you might try stacking base gaskets to lower the compression. This would be cheaper than buying a new head. This will raise the port timing slightly which will ease the bottom end a little also. This can help make it easier to ride.

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Bogging 50
Dear MX Tuner - My son has a Husqvarna 50cc Sr..  Husqvarna has replaced the coil stater three times and this last time they replaced the fly wheel and the coils stater.  it just dosen't seem to be running right.  Sounds like it is bogging down and someone said that it could be the timing, the jet or the front end needing to be rebuilt.  We would like to be able to maintenance the bike ourself.  How do you adjust the timing?  I don't even know what question to ask about the jet.  Surely it wouldn't be the front end - he got it last Christmas and has not ridden it that much. He has a Yamaha that he races too. Also, is their a manual that would help us with these problems?

Thank you. Karen

Husqvarna should be able to supply some sort of manual for your 50. This should give any info concerning changing the timing. The timing is adjusted by rotating the stator plate but timing too far advanced can result in a motor that burns holes in pistons. I think whoever said the "front end" needs rebuilding probably meant the "top end". I doubt if this is the problem. Chances are repacking the silencer and rejetting the carb will help with the bog. Eric Gorr has a good two stroke jetting guide on his website. Go to for more info.

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1982 Kawasaki KDX 175
When the bike runs, it runs very well. It burns clean, has excellent throttle response, and good power through the entire throttle range. There are no out of place noises or odors. The trouble is, it doesn't run very often. Even when it does run, it is impossible to kick start. It needs to be push started. After a couple seconds of dead revolutions, it will finally come to life, if it is going to start at all. Once started, there is no certainty as to how long it will continue to run. I believe the problem to be eletrical. When it doesn't start, the plug is wet and I can not get it to spark after it has been removed. The coil tested good. I can measure a voltage from the stator and ignitor, but I do not have a repair manual and have no idea what the voltmeter is telling me. I bought the bike used and every wire has been spliced. I have traced all of the wiring, removing the excess, and insured there are no shorts. It is obvious that the engine has been apart and the wear on the screws suggests that the stator and ignitor are not original and have been removed several times. I can find a stator but have been unable to find an ignitor. Is there anything else I can do or is it time to buy another bike?

A service manual will give resistance readings to check the ignition components. You might try cleaning all the grounding points for the whole system. Corrosion or paint under a mounting tab can give some erratic symptoms. Just look where the coil mounts and any ground wires.

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Sprocket Selection
Hello Mark, I have a new Honda XR650L and I am a beginer at off road riding.  I bought the L so I could ride up the street to get to the trails.  I don't like the way the motorcycle is geared.  Where I ride and starting out slowly I don't use anything beyond second, and when I am in the slow stuff I'm usually sliding the clutch in first. I realize the top speed of this motorcycle is at least 70 mph and I don't ever expect to go than fast on or off road.  Could you give some basic guidelines on making a sprocket slection.  I looked at the specs for some other Honda models and see they use other ratios.  I would like to just change the front sprocket because of cost and wrench time.  Also this model uses a one piece chain so how does dropping a couple of teeth off the front sprocket affect chain adjustment.  As for the parts is this a dealer only item. Any help would be appreciated.

Thanks, Rusty Gentry

Sunstar and Renthal both list a 14-tooth sprocket available to replace the stock 15 tooth. Sprockets are not a dealer only item. This will give a substantial lowering of the gearing. This should be able to be adjusted without cutting the chain provided the chain isn't too stretched. Even with the lower gearing, your 650 should still do well over 70mph.

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Clutch Slip
Have a 1999 KX500. Clutch is slipping but only when I run the bike for a few hours. The bike is tuned and hopped up to the limit pushing 75+ horsepower. I inadvertently dumped Belray gear saver 80W in the tranny which is for my friends bike. I should have been using something like 30 or 40W. Have I caused the problem? Am I doomed? I pulled the drain plug last night and left it out. I am thinking if I just let it drain a few days and put the correct oil in I should be okay? Or, do I need to pull the cases off and clean/replace the discs?

I appreciate the advice.

Sincerely, Stupid KX500 Rider

You should be fine by using your favorite oil. You might have to drain it after a few minutes to restore your original clutch action. I've found Type F automatic transmission fluid works very well, especially for KX clutches. It actually improves their feel. The ATF provides excellent lubrication protection and helps shifting also. I'd change it every few hours, regardless what you use.

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Comment On This Article

Bog Standard - 1991 CR250
Not so much a problem. I just need a bit more power to keep up with my mates XR600! The engine is in mint condition and is pretty fast as it hasn't done much for a 10 year old bike. All I have ever done is replace the piston rings about 4 years ago as a precaution and put in a Multi-Air air filter. I think the first step is an FMF Fatty pipe and carbon reeds(or perhaps a rad valve?). And perhaps get the barrel tuned for more top end as it is very torquey. Is this the best way to go? I have also seen some companies advertise big bore kits to 265, 285 and even 300cc. Is this a good idea and would it be relaible?  Your opinion would be much appreciated.

Thanks, Alan.

Some of the big bore kits can reduce reliability and increase vibration if you go too big. The 2mm over kits are great. That would be the 265cc motor. Those help more than you'd think 2mm would. Eric Gorr is the master at doing these. He'll also port the cylinder for your personal preference at a bargain price. His work is second-to-none. Go to for more info. Another very cost effective mod is a Delta V-Force reed cage. Once jetted with the new reed, you'll be quite surprised at the improvements they make. The stock Honda pipe is really pretty good. An FMF pipe will help it rev higher.

I'd replace the piston. 4 years is about 2 years too long to go for a bike that is casually ridden.

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Beached XR
I have a Honda XR400R 1997 model which I am having difficulties with.

Following a beach run, which involved sea water crossings, the bike back-fired and would not restart.

I have since managed to start the bike however it only runs for a short time (APPROXIMATELY 5 - 10 MINUTES).It then back - fires and will not restart.

I have completed a number of routine checks which have proved unsuccessful in finding the route of the problems. i.e.air filter, carburettor, and spark plug. I did locate oil in the left hand side casing cover which contains the rotor and stator coils. I would be grateful if you could assist with the following questions:

a) Should there be oil within the casing cover described?

b) If not - could this be the cause of the problems I am experiencing?

c) Do you have any other suggestions as to the source of the problem?

I look forward to your reply and would like to thank you for your assistance.

Yours in anticipation


The oil around the stator is normal. Sounds like you have some water that got into an electrical connector somewhere and has corroded causing an open circuit somewhere. You say "sea water". I take it this means salt water.  This is very corrosive. Definitely check any and all electrical connections.

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2001 CR500 - Piston Slap?
i bought bike brandnew,cant have more than 5-6 hours on it,broke in very easy,still has good comprision,starts very easy, seams to run great slow or  fast,will ideal just fine,no noticeable runing problems..BUT,,when cold or  hot,when i rock bike back&forth in gear,has loud piston slap type noise so i  took off pipe and with fingers in port i can move piston back and forth what  feals like 20 thou of an inch or what feals like half width of the ring,,i  think clearance should be 4 thou of an inch.please help,could the factory  have over bored it or to small a piston..p.s. any input would be appreciated

I'm a little unclear which way you're moving the piston to get it to move. If it isn't making noise when it is running, I wouldn't worry about it. You may be hearing the chain slapping the swing arm.

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1997 KX125 Carb Tuning
I am having trouble with my bottom end acceleration. I Bought this bike from a gut that lives at 11,500 ft elevation, I live at 5,000 ft. It had a 155  main jet in it, boy did that spit oil all over the place! I replaced it with  a 145 but kept fouling plugs. I finally replaced the jet with a 140, seems to  have worked so far. The biggest problem now is bottom end acceleration. That  bike runs like a raped ape at top end, but I have to stay on the gas all the  time to get any power. I was reading about the slow jet, but can't seem to  get enough information to convince me. I need to know if a different slow jet  will help and if so, what size do I need? Got any ideas?

Convincing? Your bike doesn't run right and you need convincing? With the 140 main jet, you're going to nuke your top end. You need to go closer to stock and rejet the pilot (slow) jet. Try for a good two stroke-tuning guide.

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Sorry if this is the wrong place to send this.  I have a 98 rm 125 that keeps overheating.  It will send coolant pouring out of the overflow in  the neck of the radiator.    one persone told me I was running too lean  so I raised the needle valve up, it is now in the second from bottom clip.   I have the air screw out 1 1/2 turns.  The stock jets are still in it.   I just recently put my stock pipe back on due to damage to my FMF fatty  pipe.  I also just recently put boyeson reed valves in, replacing the stock  reeds.  two times now I have had to replace head O-rings empty all the water  out of my pipe. LOL  I replaced my radiator cap with one off of a kx60 after  the first set of melted head O-rings. Why a kx60?  It is all I had on hand.  I just switched from Klotz r-50 pre to castor 927.  Could any of these changes  be the problem?  Or someway combine to be?  Could you e-mail me back if  you can,  Thanks 

Randy in Dublin,  VA

The Castor 927 isn't the cause of your problem but I wouldn't suggest running it unless you plan to rebuild your top end once a month to remove the residue build up.  Chances are your head is warped. You can true it with a piece of emery paper taped to a flat surface (piece of glass or marble). Spray the emery paper with WD 40 and start rubbing the head in a figure 8 pattern. Run it over the emery paper a few minutes and clean it off. You can see the pattern where it is touching the emery paper and where it isn't. Continue until it has touched across the entire head surface. Oh, and get the correct radiator cap unless you have a specific reason to run a different one.

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Oil Seal Replacement How To
rm400 suzuki early model air cooled. i, need to know if i need to split the cases to replace the oil seal's on the crank shaft or what????

I don't know. A service manual will provide you with all kinds of good info.

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Bottomless CR480
I am a long time rider at 33 years of age. My dirt bike is the 1983 Honda CR480R. It is in very good condition for being 18 years old. My question is about gearing ratio's on this bike. The drive sprocket is a 14, and i changed the rear from a 54 stock to a 46. That means a ratio jump of .259 to .304. My concern is the long term affects on this older Elsinor engine. Its a big jump and i was just concerned about "stressing" the engine (air cooled)....What do you think ???

My main reason for changing the gearing was to make second gear faster for tracks. I am usually doing alot of shifting between 2nd and 3rd because once yer in power band then there is no top end power AT ALL. and second gear always seemed a little slow for me. Attached is a pic from S.I.R (Seattle International Raceway) in july of this year.

Any help would be appreciated,


The motor will handle the gearing change just fine. I think I might look a little closer as to getting more top-end out if it maybe. The 480's I remember had plenty of top-end.

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Burning theTranny Oil
I have a 1974 Yamaha D/T 175-A. It is burning the oil out of the tansmission. what is causing this to do this? what parts do I need to fix it ?  Thanks for your help   Ray

It's either your right side crank seal or the center case gasket. My money is the right side crank seal. You should be able to get by with a right side cover gasket and the new seal unless you open a can of proverbial worms.

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2001 Yamaha YZ125
Problem: Black oily residue coming out of the end of the silencer and dripping all over the swingarm and bottom side of silencer. Gas/Oil mixture I am running is 1 bottle(pint) Yamalube 2YR racing oil to 5 gallons of premium gas  (40:1)

Performance:  Bike runs very strong and does not blubber. Plug is slightly dark like it is a little rich.

Corrective actions taken so far:

  • I have moved the needle jet clip up one notch from the middle setting in order to lean it out slightly.
  • Backed the idle air screw out slightly.

Results: Bike still runs strong but no difference in oily residue on bottom of silencer.

Would appreciate any ideas on what may be causing it and additional things to try.


Your low speed jetting is too rich. Lean the pilot jet a step or two should help significantly. Also, unless you're truly running extended high RPMs continually, you'll benefit from running a BR8ES.

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Comment On This Article

Failed Water Pump
I have a 1996 KTM 300 EXC. It has a Boyesen Reed assembly and a FMF Knarly pipe w/and Answer silencer/Spark arrester but is otherwise stock. I love the bike but on my last ride the water pump seal went bad and loaded my bottom end with coolant. I did not notice it until the overflow tube spewed oil/coolant all over the  engine. The engine showed no signs of overheating from a riding stand point even though I rode many miles with no coolant and a tranny full of oil/coolant. 

My question(s):

  1. Other than replacing the water pump seal is there anything else I should look for in the way of damage?
  2. In a KTM 2 stroke what type and weight oil should I use in the tranny?
  3. Do you have any jetting suggestions for slow riding trails at 3,000 to  5,000 feet el. in N. Ca. as currently it drools alot out of the tailpipe?
  4. What coolant should I be using? Thanks for your help

The clutch plates could fail due to the coolant. The coolant can actually dissolve the glue that holds the fiber to the plate. This is usually after being run for a long time (much more than an afternoon). If it isn't running poorly, I wouldn't tear into it. It'll most certainly let you know when the top end is damaged.

You can use just about any 10w40, 15w50 motor oil, 80w90 gear oil, motorcycle specific gear lube or Type F ATF in your gearbox. Personally, I'd use Mobil 1 15w50 synthetic motor oil in your KTM.

The stock pipe had a problem with the stock 360 exhaust having too small a diameter at the pipe where it goes into the silencer. Dyno-Port made an excellent pipe and silencer, which made the bike much easier to rejet. Plus, the first 360's had a cylinder head that was updated right after production began. So, the first 360's would benefit greatly from installing the updated head. Check with your local KTM dealer for the casting marks to identify which head you have.

I've never had any issues running standard automotive coolant. If you have a bike that runs hotter than it should, and has trouble overheating, you might want to consider running Red Line Water Wetter or Engine Ice coolant. But for all other bikes, I'd recommend Prestone Low-Tox. This is the "pet safe" anti-freeze/coolant. Most conventional coolant is ethylene glycol. Low-Tox is propylene glycol; the same stuff Amsoil sells for $25 a gallon as high performance coolant. Good stuff.

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