Technical Questions? Ask MX Tuner
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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yours faithfully Sam
The two carbs you refer to are similar but do have different characteristics. You should be able to make your CR run well with either one once it is jetted. Plan on having to fine-tune the jetting regardless of what you're told to start with.
100 or 125?
I bought the bike after it had been sitting up outside for a few months and found that it had rain water in the tank and carb. The previous owner said it ran fine before he let it sit. I drained the tank and took off the carb and drained all water from the bowl plug and reinstalled it and it started fine with fresh gas.
The bike was responding to throttle and idling fine for the first minute but started to rev up uncontrollably and would red line if I didn't shut it down. I'm thinking this is a carb adjustment problem. Can you help steer me in the right direction?
Thanks for your help.
Check the fuel tank for rust. Remove the petcock and check inside for rust or some other obstruction. I'd highly suggest running an in-line fuel filter between the tank and the carb. Check the carb itself for a plugged pilot circuit or a float that is stuck shut. For one reason or another, it is running on too lean of a fuel/air mixture. It is probably a fuel supply issue, a clogged jet or passage or possibly even an air leak. An air leak could be around the carb to cylinder rubber boot (look for cracks) or even a left side crank seal (under the flywheel).
You can look at the base of the cylinder for a casting indicating what the actual displacement is. Look at the side of the cylinder for either a "99ccm" or a "124ccm" for the size of the motor.
Can I repair my
Really thanks - Hernan.
I've never seen any diagrams from any manufacturer that shows the circuitry inside a CDI. The only other option besides a factory replacement (new or used) would possibly be an aftermarket ignition like a Wolf.
With this information, do you think I'm going about this correctly? The bike ran fine before, so I can't believe it's jetting issue, plus the problem only happens at idle. It's been cold and wet up here in Northern California, maybe in the 40's, but I wouldn't think that would have much to do with the idling problem.
Thanks for you time, hope this wasn't too lengthy, just wanted to give you all the facts!
Thanks for being thorough with what you've done so far. I'd much rather have too much info that not enough.
The head pipe will turn red after a short period of idling. That is normal and doesn't indicate a problem. Just don't let it idle for that long.
Sounds like you're on the right track. Check one other thing while you have the carb apart. Look for a cracked slide. Otherwise, I agree about it not being a jetting issue since it has run fine before this. If it was a problem due to the air temperature, a slight adjustment of the pilot screw would cure the idle issue.
thank you - rob
Step one is go to your Honda dealer and buy the factory manual. There is way too much info in that book to not have one if you're into it that deep.
thank you vey much
Your Suzuki will do nicely run at the ratio of 40:1. Use a good quality two-stroke motorcycle oil. I'd stay away from outboard motor oils.
Resleeving is one of the worst ways of repairing a plated cylinder. You can get a damaged cylinder repaired for less than the cost of either a replacement cylinder or a resleeve. Resleeving alters the heat transfer characteristics of the motor.
I'd check the power valve to make sure it is operating correctly. On the left side of the cylinder (as you're sitting on the bike) there is a round cover (it has a 17mm bolt head). You can remove this cover and watch the end of the power valve move as you rev the motor. It should begin to rotate at about 4000 RPMs or so. Basically, just check to make sure it is moving. There is an "L" and an "H" mark that the slot in the end of the power valve will line up with. "L" is the low rpm position and it should rotate to line up with the "H" when it is revved.
AVGAS vs. Race
Avgas won't give any performance gains over premium pump fuels. It's almost a trade off since it isn't formulated to run at anything similar to a two-stroke dirt bike environment. The octane rating is figured differently than pump fuel. An airplane engine is meant to be run at a much more consistent rpm and at a lower rpm range also. That being said, it won't harm anything in your motor and may be a decent source for a consistent higher quality fuel if you're having trouble getting good fuel from local stations.
Pipe for Honda
I'd check with White Brothers and see what they have available. They have a wide variety of applications and are some of the better designed and built systems available. They have disc type exhausts similar to a Supertrapp.
I have had limited success having the drain plug casting welded. It can be difficult to weld since the metal needs to be clean and oil-free. Another thing that may happen is a leak may develop at the seam between the cases due to the extreme heat causing expansion and contraction during the welding process. This is a risk you need to think about. If you don't repair the case, you should to disclose this to any prospective buyer.
A mechanic friend of mine has:
What should we look at next?
Kind Regards - Ed
The only other thing I can think of that might give that symptom is the carb vent hoses. If they get clogged, they can do exactly that. You need to determine whether it is losing spark or not. This obviously will take you in one entirely different direction.
Torco is not a bad oil. As long as you're running at 40:1, you should be okay lubrication-wise. I think I'd take a close look at the air filter and the way it seals in the airbox. If it sucks any dirt, that'll ruin crank bearings (among other things) quicker than anything else. A dead giveaway if an improper sealing air filter is traces of dirt in the boot going to the carb. It ought to be 100% spotless, otherwise you have trouble getting ready to happen.
The spooge is due to a combination of things. One is the jetting being too rich. You need to lean the lower speed circuits. Start by leaning the pilot jet a size or two until you get some eye opening throttle response. This will cut down on some of the spooge. The other thing you can do is run a BR7ES spark plug. This plug is one step hotter and will help reduce/eliminate the spooge.
Check with Thumper Racing or White Brothers. Both offer aftermarket mods that will do good things to your KLX.
Yes, running a motor jetted too lean can cause a seizure. But this would be during a sustained high rpm run. This would be caused by a main jet that is too lean. A pilot jet or needle won't cause any seizure related problems. You can experience a bog that is caused by a lean condition but you won't experience any damage. A good starting point is the center position for the needle clip.
Tweaking My 125
Your CR does have the potential to run with most anything out there but it may take a few more mods to get there. You need to run an aftermarket reed cage. My choice would be a Delta V-Force. This reed cage just plain works and works great. The next step will be a good porting that can fine tune the power output to your liking. Don't go with one of the big aftermarket companies since you'll get a "cookie cutter" port job. Expensive and not tailor fitted to your needs. I highly recommend Eric Gorr. He is undoubtedly one of the best in the business. You'll get a better job at a cheaper price. One other option is a 2mm overbore. This will put it in the 133 cc area. Still legal for AMA amateur competition and a big gain in overall power. Eric can help with that also. Go to www.eric-gorr.com for more info. Tell him Tuner sent ya.