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I just recently bought my son (very small 14 yrs) he moved from a crf 80. My question is: This bike surges ALOT and i guess it is because its a race bike....however, i bought the bike mainly so he can ride anywhere. But it seems to lerch alot because he cant seem to find that perfect throttle area to keep the rpms steady when he is in lower gears and or at lower speeds. He is new to power and the bike has plenty....i just need to see what i can do to regulate the power more evenly. Again, i know this is a race bike...however the trail bikes were way to heavy for his little frame and weight. He loves the bike..but the bike lurchs back and forth because he cannot find the sweet spot because the throttle is sooooo sensitive..help plz

Surging, if my memory serves correct, is a symptom of lean jetting. In my opinion, the bike comes too lean from the factory. If you have never changed jets, it really is easier than it sounds and the first time is the hardest. I won't spend time telling you how to do it now if you already know (if you don't, just say so or look at the "450x jetting change" in the "how to" section). The stock main jet size is 135, I am currently running a 138 or a 140 depending on temp. and a 48 pilot jet (I think). The power is still very strong but is smoother- easier to ride, in other words. The bike also runs cooler (good for tighter riding) and starts easier.

Another cause of a lean condition is a under oiled air filter, an air leak in the exhaust (loose bolts), air leak in the air boot or intake mainfold between airbox and carb and carb and cylinder head. Make sure those bolts are tight then try the jetting changes.

Good luck and hope this helped!

I am not a fan of them, but the Flywheel weight was made to fix exactly what you are describing. I don't like them because they take a little of the hit off, but again that is what you are looking for. Isn't there a way to tighten the throttle friction?

If he is not riding with a finger on the clutch lever he needs to learn that technique. Smooth clutch actuation and release will keep a smooth delivery of power to the rear wheel regardless of what the engine is doing and will control the lurching. When the clutch lever is completely released and just using the throttle to deliver power to the rear wheel you will have the lurching you discribe on a spirited bike such as the 150R. Feeding the power of the reving engine to the rear wheel smoothly and evenly by sliding the clutch a little will eliminate the lurching. Sounds easy. A little practice and patience will pay off. Try putting the bike on a stand with the engine running have him put it in gear and practice throttle control and power delivery with the clutch lever.
O.D.

Collin wrote:I am not a fan of them, but the Flywheel weight was made to fix exactly what you are describing. I don't like them because they take a little of the hit off, but again that is what you are looking for. Isn't there a way to tighten the throttle friction?

I agree with Old Dude. Collin, the fly wheel weight adds rotating mass to the crank shaft, which slows down how quickly the bike can rev. That slows down the power out put from top to bottom. Surging, as he describes it as, would imply that the upper and lower parts of the power band are more controllable but from bottom to mid and mid to top it jumps, or surges. Sounds like jetting and, like Old Dude said, clutch control. Get a flywheel weight if you want less wheelspin; work on throttle control, clutch control, and the jetting if you want to fix surging.

My dad actually cut a piece out of the outer edge of the throttle tube. He did this to cause more friction so I wouldn't hit the throttle on bumps. Worked for me.

maybe try a smaller rear sprocket to giveit less bottom or a fly wheel weight. i always have trouble in the parking lot of a track on my bike becuase it jut wants u to gas it, but unfortunaly u cant always, so the best thing to do in those situations is use the clutch and throttle to keep it running calm.
also, a little work out routine never hurt anyone

Collin wrote:My dad actually cut a piece out of the outer edge of the throttle tube. He did this to cause more friction so I wouldn't hit the throttle on bumps. Worked for me.

someone on thumpertalk siad they did this to their kids bike