hesitating/jerking at full/open throttle

[Chinabike]

I'm not sure what going on with my 125cc now, might anyone know?
The bike is hesitating/jerking at full/open throttle at the end of any gear.
Maybe to lean or rich. The only thing i did was reroute the throttle cable.
I tried putting 115 jet in but still same issue.

any help.

[culcune]

Something simple like a spark plug?

[Chinabike]

Something simple like a spark plug?

I tried a new one but it still happens, the plug says it's on the richer side.
I might try one more new plug. But it seems/feels like its getting to much air or gas. Like a surge/jerk when I try to go full throttle at the end of every gear.

I might try a 120 jet. or play with the needle clip.

[Chinabike]

Something simple like a spark plug?

Had to check!!! Yep! i think it was the plug.
I don't think the plug was screwed in all the way or loses. just took it out for a quick ride and ran great. I think when I installed the oil cooler the new plate that attaches to the head for the oil lines doesn't let my spark plug socket fit all the way over the plug to turn. just slips.

I should of known i tried to install a NGK spark plug boot the other day but it wouldn't fit over plug because the oil cooler plate hangs over the plug hole like by 4mm

I'll give it a better longer ride tomorrow to be sure.

Thank you culcune!!

[ChrisWNY]

Make sure you're using a spark plug socket to tighten it up with your ratchet. The plug needs to be snugged into the head but not over-torqued like you're tightening down a rear wheel.

[culcune]

Had to check!!! Yep! i think it was the plug.
I don't think the plug was screwed in all the way or loses. just took it out for a quick ride and ran great. I think when I installed the oil cooler the new plate that attaches to the head for the oil lines doesn't let my spark plug socket fit all the way over the plug to turn. just slips.

I should of known i tried to install a NGK spark plug boot the other day but it wouldn't fit over plug because the oil cooler plate hangs over the plug hole like by 4mm

I'll give it a better longer ride tomorrow to be sure.

Thank you culcune!!

No problem; my first Chinese bike, an Alpine enduro (Alpine was a sister brand to Jetmoto like Mercury and Ford--both Alpine and Jetmoto are long gone) I had what seemed like a catastrophic failure on a ride. It was a fouled plug. So with any kind of miss or whatnot, I always suggest starting there, which you found out was your easy fix! :tup:

[Chinabike]

No problem; my first Chinese bike, an Alpine enduro (Alpine was a sister brand to Jetmoto like Mercury and Ford--both Alpine and Jetmoto are long gone) I had what seemed like a catastrophic failure on a ride. It was a fouled plug. So with any kind of miss or whatnot, I always suggest starting there, which you found out was your easy fix! :tup:

I spoke too soon, Still happing but it seem to work better with a new plug
Still, right as I get to full throttle. hesitation/jerk
Could it be the throttle cable? that's the only thing I can think of.
when I changed my bars I had to reroute it because it was to short.
But it seems like it has plenty of slack now.

[bogieboy]

Check and make sure the wiring to your CDI box is plugged all the way in, and also check to make sure your coil isnt loose on the frame... i have had both of those scenarios cause misfires and poor running...

[pete]

Rev limiter ?


..

[Merlin]

You need to re-jet your carb.

[ChrisWNY]

I spoke too soon, Still happing but it seem to work better with a new plug
Still, right as I get to full throttle. hesitation/jerk
Could it be the throttle cable? that's the only thing I can think of.
when I changed my bars I had to reroute it because it was to short.
But it seems like it has plenty of slack now.


Could be a jetting issue with the carb - this can happen if you're running too lean (engine starving for fuel) or too rich (engine can't burn the fuel fast enough at full throttle). A lean engine will run hot while a rich engine will run cooler.

Your spark plug is the best indicator of what's going on - next time you're at wide-open-throttle, pull the clutch (while the throttle is open) then immediately kill the engine while holding the clutch. This should be done when you're riding the bike. Don't let the engine fire, use the brakes to slow down and stop. Pull your spark plug...if there's white residue and it looks very clean, the fuel mixture is too lean and you'll need a larger main jet. If your plug is badly fouled up (black/oiled up) you're running too rich and you'll need a smaller main jet. You can always take a photo of your plug and post on here so others can help diagnose.

[Chinabike]

Thanks ChrisWNY I'll try the method in the future.
Ya, i checked the plug before it was on the rich side.
I didn't think it was the carb because it was running fine a day prior.
BUT! good news

So searching interweb last night and came up with a possible cause...too loose of chain. Yep! My chain was pretty loose didn't seem that bad. but i belive the spec on the hellcat 125cc chain slack is 15mm-20mm my was at like 40mm play.

I tighten this morning and give it a quick ride and ran perfectly. I'll give a longer ride tonight when I have time.

[ChrisWNY]

If the chain tension was an issue check the sprockets too...check for uneven wear and damaged teeth. I haven't personally experienced engine hesitation or throttle issues on the top end due to chain tension. A chain that's too loose can jump the sprocket and do all sorts of damage especially if it works its way off and you're in gear applying the throttle (see image below...).


https://s33.postimg.cc/f0btf426n/loose_chain.jpg