I have a honda sky (sgx50) and it has recently started revving very high on idle (equivalent to about three quarters full throttle) for about five minutes and then stalling when the engine heats up. After checking the carburetor assembly I could find nothing wrong. I suspect the auto choke as the carburetor seems fine and although the throttle cable has a bit too much play in it, it functions well enough and doesn't explain the high revving from idle. I'm somewhat stumped as it the engine is acting like the throttle is stuck open, but there are no physical symptoms, at least not in the carburetor.

I understand there is a throttle stop screw that might be holding it too far open, but I'm not sure I know which screw this might be.

Would appreciate any input from anyone reading this.

Niall

Niall SIngers, April 2008

Its almost certainly an air leak, most likely th rubber seals either side of the crankshaft, change both, you will need special pullers you can maybe borrow them from your local honda dealer i did

merovingian, August 2015

Gasket leak in the cylinder head is another cause of revving

Pepsodent, January 2012

firstly the idle screw is on the left of the carb and you can get to it with a screwdriver just turn it anticlockwise to slow he idle speed and the mixture screw should be set 1 ans a half turns out to one a and three quarter tunrs out, the most likely thing to cause the rise in revs is the throttle cable being too tight make sure you have some free play in it at the twist grip there is an adjuster on the cable up there to give the free play it needs you will need a 8mm spanner and a 10 mm spanner

adam, April 2008

the throttle stop screw is on the right of the carb it the only one going into the side of the carb and just holds open revs so have a play with it you cant do any damage but i would have to say you need a new jet. they get smaller over time letting more fuel in and making your bike rev high

Dave, April 2008

There is indeed a throttle stop screw, spring loaded that fits into the carburettor throttle slide - the round chamber below where the throttle cable fits in through the top. Unscrewing this should drop your revs down. I've no idea why it should suddenly start doing this though. As you close the throttle you should hear the carb slide hit the stop with a slight click if its seating correctly. There also could be a smaller spring loaded screw in the carb body too - this is the idle fuel mixture adjustment. Screw it in fully and then back out 1 turn is the usual protocol.

John, April 2008