Engine Reving- Clutch Engaged

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.

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.

http://motorbicycling.com/f39/installing-carburetor-manifold-your-motorized-bicycle-303.html

check this out.
Norman

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.

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

You might check the cable housing at the carburetor. Mine sometimes jumps out of place and causes the engine to rev uncontrollably. Fixed it with some duct tape, wrapped arount the cable housing were it meets up with the carb.

hi norm -glenz here, hey, do you know where to get a pull start for an 80cc-jet? also,where do you get the aftermarket paper air filters? thanx. i've got the same revving problem with mine,seems like it started after i changed the fuel line to reg. auto line. i have a bear of a time trying to get a clamp on it at the carb. is a clamp really needed there?

Glenz
I don't know where you would get the pull starter you might try looking at the vendors here on the side of the forum lot to look at same for the filters.
I still run the cheap vinyl fuel line and use .031 safety wire as hose clamps if the line leaks. I change out the line as it becomes brittle.
Norman