Engine Reving- Clutch Engaged

Hello All,

So i have read several post focused on adjusting the idle control screw on the side of my 80cc 2 stroke carb. My idle, (not twisting the throttle while riding the bike, clutch disengaged) is great, however, when i engage my clutch to roll in nuetral (while at a stop) my engine revs really loud. Any ideas? Thanks much. A noobie.

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You have an air leak somewhere between the carb and the cylinder. To find leaks I spray carb cleaner around the area and when the engine slows down or starts to die then I know I found the spot it is leaking at.

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Thanks! this engine is brand new, ran less than 2 hours... ill check for leaks tomorrow, I was hoping it could be from my throttle cable being too taught. Appreciate the help!

That is possible too. It is difficult to troubleshoot something without seeing it for yourself. Usually when a motor revs hard seemingly all on its own it is an air leak. Often the carbs leak where they connect to the intake pipe. Myself and others use an O ring there to prevent that. SBP's sells the O rings. It is possible to have a leak at cylinder as well.

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installing carburetor on manifold of your motorized bicycle engine

check this out.
Norman

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Air leak it is! Thanks much guys!

maybe you just need to turn your idle down some. with engine idling and clutch disengaged in your driveway turn screw counter clockwise until engine almost stops.

the screw is only for idling at a stop,not for riding,thats why it runs fine when riding and when you stop ,it idles high,adjust your idle lower.

when i had a exhaust leak(like when my gasket blew out) my idle stayed the same.

Thanks guys, i'm still having an issue and my checked my carb and its connection, its sealed up tight. As for the exhaust im not positive, i will check tonight and get back to you.

As for the idle adjust screw... I'm frustrated to all ends with that thing, I have sat in my driveway, motor on, clutch engaged, (Motor Revving uncontrolably) and screwed that thing the entire way out till it fell in my hand and no adjustment to the idle was made.... Am i missing something here? I know this is basic small engine mechanics.. ive never been so stumped! Thanks all for the help!!!

take your air cleaner off and look inside at the throttle slide will it go completely closed?(it should) Then start screwing in the idle screw and watch the throttle slide . With the throttle slide all the way closed start screwing in the idle screw it should make the throttle slide start opening but only a tiny bit.
sometimes the throttle slide will bind causing a run away or high rpms . The cap on the carb if over tightened will cause the slide to stick.
Is you throttle cable tie wrapped to the frame or the handle bars? another cause of high rpms at idle. You need the cable to be able to move freely. move handle bars side to side and watch the throttle slide see if it moves.
Throttle cable too short not allowing throttle slide to go completely closed? need to redo the throttle cable by shortening the outer housing only or replacing the throttle cable.
this is just some of the things to look at.
The last item would be the twist grip when you open it up and let go of the throttle it should snap shut by itself. Paint on the handle bars will cause the twist grip to stick. Sand off the paint under the twist grip do not oil or grease that area either.
Let me know how its going.
Norman

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