Engine revs after throttle is released, 66cc china

J

Jimmytonga

New Member
So recently a few problems have arisen, and I think they may all be related to one another.

First off, my bike used to be incredibly easy to start. Now it takes like 20 seconds of me pedaling with the clutch engaged and the throttle wide open. But I can live with that.

The second problem that I have is that after riding for a bit, when I let go of the throttle and pull the clutch in order to stop, the engine continues to rev for sometimes a good minute before slowly going back to idle. This is extremely annoying and kinda scary to be honest.

The third problem is that I have to keep my idle incredibly high in order to keep my motor from dying. The Idle screw is almost screwed all the way in. this is also really annoying.

Thanks for any help!
 
Start looking for an air (vacuum) leak in the intake area. Usually it's either the carburetor attachment to the intake manifold or the gasket at the cylinder and the manifold.

There are other areas to check but these are the most common. Cranshaft seals can also go bad giving the same symptoms.

Tom
 
Thanks for the reply!
Ok I checked everywhere for a vacuum leak and i absolutely cannot find one!

I sprayed wd40 all around the intake manifold/carburetor attachment and also all around the intake gasket, neither of the places affected the idle in the slightest bit. I also sprayed all around the crank case seal and nothing affected the idle either. Finally I checked for oil leakage under the magneto and there was none.

Also just as a shot in the dark i pulled the air filter off and checked the barrel response in the carb and it was perfect.

The symptoms point to an air leak but I cant find one for the life of me!
 
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Take a look at your carburetor throttle mechanism. It would help if we knew which carb you have. If an NT, remove the air filter and look into the throat while twisting the throttle grip and watch the cylindrical part lift then drop when you release the throttle. It should move smoothly to the almost closed position.

A binding throttle cable or one that is attached to tightly to the frame, or has sharp bends can bind holding the throttle open. The cable end could also be binding in the twist grip. The part the cable wraps around is called the thimble. They sometimes require a little trimming to allow the cable to wrap and unwrap smoothly. A little lubrication in the cable housing can help too.

I'm no expert on the CNS carburetor and maybe someone who knows it better than I can chime in and tell you what to look for if you have that style of carb.

Because your engine suddenly became harder to start still leads me to believe you might have an air leak somewhere. If the throttle works properly, keep checking. There are two crankshaft seals. One behind the magneto rotor and the other behind the primary (small) gear on the right side.

Good luck and let us know what you find.

tom
 
turning the idle screw all the way in is often a rich condition - when it happens suddenly, I look for a small piece of crap stuck in the float needle or a float that has sunk due to fuel leaking into it

a blown seal can also act like this sometimes
 
crassius said:
turning the idle screw all the way in is often a rich condition - when it happens suddenly, I look for a small piece of crap stuck in the float needle or a float that has sunk due to fuel leaking into it

a blown seal can also act like this sometimes
Click to expand...

I had a bad bowl seal do this once, but the fuel all over the carb gave it away :). Still, check everything. An air leak would make the bike run lean, so i suggest a plug chop. If it seems like its running lean, that is 1 more point for air leak. If its a nice color, then its a mechanical problem somewhere.
 
Thanks for all the replies!

Well I checked my plug and it looks tannish dark grey, which I thought was about right, maybe a slight bit rich. Also I checked the throttle slide and it is working fine. Also I took apart the carb and cleaned it out. So I'm officially clueless...

It also might be worth it to mention that Im running opti-2 at 75:1

I might just replace the crankshaft seals or the carb, just to be sure. Which should I do first/Is there a good guide on replacing the seals?
Thanks
 
Try this> http://motorbicycling.com/showthread.php?t=46230 or type in 'crankshaft seals' in the search box. There's lots to read on the subject.

Just curious why you're running your oil mix @ 75:1 instead of the recommended ratio?
You're a little oil rich with Opti-2. Try 100:1 and see what happens. I think you'll like it.

Tom
 
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