Unstable idle speed By lencho (Read 9,781 times)

[lencho]

While waiting for the delivery of a new spacer and gasket, I decided to take kz1000st's advice and check the valve clearance. The intake was set at .0025 and the exhaust was tight with no gap. Set both valves at .004 and all is good now. She idles like a sewing machine at 2000. The only explanation I have is the the exhaust valve wasn't closing completely and allowing exhaust to be drawn into the cylinder during the intake stroke resulting in a lean condition.

Thanks kz1000st and everyone else that gave advice.

Lencho
;D

[Bashan]

Good grief man, now KZ's head will be so big he won't be able to fit through a door! Your explanation of how the gap was affecting the engine is spot on. Also, the open valve was compromising the compression and it only gets worse as the valve expands with heat.

[sledwrecker]

Also check your intake boot where the clamp holds it onto the carb. It will sometimes develop a crack there from being tightened down too tight. Mine looked fine from the outside but when I took it off the bike and inspected the inside of the boot where the carb fits in I found a split about 1/2 inch wide right where the carb seats.

[donwjaco]

I saw that this was an old post, but thought I'd share my experience with my new Chinese MC-22Y-150cc scooter. For the first 120 miles it ran like a beast, top speed 55mph, very strong up hills etc. All was well until I stopped at a stop sign, it began running rough, then stalled, I was unable to start it for a good 10-15minutes, finally it started running very rough, needing a lot of throttle just to limp it back home, I was still able to get up to 40mph got it home and started searching for the reason this happened. Spark plug? Timing? Valves? Fuel flow? etc. I removed the seat and support, then the flooring to get at the spark plug and check all the hoses. After looking at everything I noticed on the floor mounted gas tank there was a vacuum hose that was not connected to a fitting on the gas tank, apparently it slipped off due to the little hose clamp not being far enough onto the fitting on the tank. I thought maybe this was it. I reconnected it started the engine and what do you know, that was the problem, a vacuum hose that had come loose. Amazing

[donwjaco]

I had trouble with idle and stalling as I accelerated with my MC-22Y-150 scooter, it turned out to be just a vacuum hose that had come off of the fitting on the floor mounted gas tank, reconnected it ran as it should, thought I as facing a whole lot of possible problems.