Engine races--idle adjustment stuck? (Doesn't work)
Have old Vespa P125X, and engine races as if idle is set way to high. I tried adjusting the idle setting, but it had no effect. What's going on? Can I fix it myself?
Beverly Joyce sounds like you may be due for a carb rebuild. I'd be getting either a complete rebuilt set or replace the Dell'Orto SI20/20 D available at places like this To get an idea of what is involved check this video To set your idle you will have to adjust two jets. The "slow running jet" and the main jet.
Oldturkey is right,
but before youdo that, look at your floater valve inside the carburetor
if it is stuck the fuel level is wrong and the engine tends to race..
possible air leak at the manifold - between the engine case and the carburator - could cause it too.
Does it drive/ride reasonable, is there throttle response under load?