Engine catching chain, misfiring, or what?

Z

zebugman

New Member
Hi. I have a problem with my bike that I can't seem to fix. I have no idea what the issue is.

When I accelerate, all the way from 0 to WOT, the bike has these weird "spits." It's like it misses one fire and it causes the bike to jerk for a split second. It does this seemingly randomly, sometimes twice per second and sometimes a few seconds with nothing. Once I get to WOT, it stops. I can't decide if it's an engine problem or if the chain is just catching somewhere temporarily then releasing. D:

Halp pl0x.
 
Sounds like a little bit of four-stroking to me. Without knowing anything about your motor etc, that's the best I can throw out there.

If it's a CG 2-stroke, that happens.
 
I'd first check for a loose motor mount or loose ign wire, but without a way to get the rear wheel in the air to run the bike while observing, this could be a hard one to fix.
 
CT: It doesn't seem like four-stroking. It's never four-stroked before. It's a recent development.

Crassius: The issue never occurs when while the engine runs with no load. D:

Also. After further testing, the more load, the worse it is. Uphill makes it spit a lot. Flat ground makes it spit every once in a while until I level out the throttle. So it has something to do with having a load.
 
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I put them on the run-bench and load them with the rear brake.

Missing under load is usually ignition, but can be an extreme lean condition - maybe your CDI is getting ready to fail?
 
I agree. If it only misfires under load and it gets worse with more load, I'd look at the ignition first.
Marginal cdi box or coil would be my guess.
Try a fresh plug too, they can get wonky sometimes.
 
You might have an air leak that is only apparent under heavy breating conditions such as accelerating.. The o-ring into the NT carb will help if that's the issue.

Does the bike suddenly have tons of torque and then go back to normal when you reduce the amount of throttle slightly?
 
It has steady torque, I'd guess. The stutters are only about one full stroke in duration and come every few seconds. It's not like it's consistent through the power band
Fwiw, my back wheel isn't credit card true.
 
If you hold your bike top bar with one hand the motor head with the other and try to push and pull your motor back and forth does it move AT ALL?
Any movement is unacceptable and will certainly fell it under load and an engine that moves will indeed case the chain to hit the case, rip the whole cover off in some cases.
 
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