High rpm problems

[-josh-]

When i take off on my bike it pulls hard up to about 20mph then it seems to run fast/loud/maybe even miss... I lose most power until it stops having a tantrum and begins to run fine again and start to pull... This happens on and off as i try to hit top speed never achieving full speed/rpm. It will not do this unless under stress while driving, wont do this with the clutch pulled and floored. I can make a video here soon to help describe its problem

 

[crassius]

could be the clutch is slipping

 

[Frankenstein]

Ate you saying that it speeds up, then makes some weird sound and possibly vibration when dying off to lower speed, then suddenly starts running fine again and speeds up? If so then...

Going to sound odd but my sister had the same problem and I was never able to diagnose what the f*** it was. Sorry I couldn't be more helpful. I personally thought it may have been a faulty sparkplug but never actually tested it. I figured that it would fire as normal until the plug got too hot and something internally was expanding and making a bad connection. Then I thought her carb was to blame for being loose somewhere like on the choke. Then thought it could be a failing cdi with a loose point heating up and shutting off and sparking only when it cooled.

Turns out that buying another kit fixed the problem since her bike pissed me off that much.

 

[gary55]

I have seen something similar to this happen when the engine is not mounted securely. It is really common. When the engine reaches the point of rpm where it starts to vibrate, with poor mount tightness it will allow the engine to vibrate violently enough to disrupt the fuel flow from the carb..

The fuel in the bowl foams, and the needle vibrates radically in the pickup tube. The engine dies down below the resonant point, stops vibrating fuel flow becomes normal, and engine accelerates until it starts vibrating again. It will continue the accelerate, vibrate, and slow down cycle with no change to the throttle.
This sounds like what your bike is doing. Tighten the engine mounts, and see if it helps.

 

[Frankenstein]

I have seen something similar to this happen when the engine is not mounted securely. It is really common. When the engine reaches the point of rpm where it starts to vibrate, with poor mount tightness it will allow the engine to vibrate violently enough to disrupt the fuel flow from the carb..

The fuel in the bowl foams, and the needle vibrates radically in the pickup tube. The engine dies down below the resonant point, stops vibrating fuel flow becomes normal, and engine accelerates until it starts vibrating again. It will continue the accelerate, vibrate, and slow down cycle with no change to the throttle.
This sounds like what your bike is doing. Tighten the engine mounts, and see if it helps.

That could be a good explanation! Didn't think of it at the time but I did notice she had problems with her mounts being tight

 

[Jonj57]

Could be it's four stroking? Engine suddenly gets a lot louder sometimes skips and you hit a power wall that you can't pass? Try to check your plug to see if it's rich if so change your jet needle or jet accordingly

 

[gary55]

Could be it's four stroking? Engine suddenly gets a lot louder sometimes skips and you hit a power wall that you can't pass? Try to check your plug to see if it's rich if so change your jet needle or jet accordingly

It could be four stroking. Then we go into needle adjustment or jetting. What lead me to mounting was when he said when it stops it's tantrum it recovers it's power, so first stop is mounts, second is carb. in my trouble shooting.

 

[Jonj57]

It could be four stroking. Then we go into needle adjustment or jetting. What lead me to mounting was when he said when it stops it's tantrum it recovers it's power, so first stop is mounts, second is carb. in my trouble shooting.

I read tantrum as just the engine acting up being loud and misfiring, but yeah if it starts to violently vibrate you have problems outside of carb world.

 

[gary55]

I read tantrum as just the engine acting up being loud and misfiring, but yeah if it starts to violently vibrate you have problems outside of carb world.

I had mad four stroking issues when I first started out with these things. Most from constantly trying diff. bolt on performance mods. and a poor understanding of a two stroke engine. Trial and error along with a few sage words form these members have been a big help.

 

[Mrmotion]

Sounds like a vibration issue I once had where the carburator perculates fuel up through the bowel vent due to vibration and gets sucked up unmetered into the engine making it run AFU, make shure you don't have any broken mounting studds , be shure to extra tighten all the engine mounts and exaust also