idling

[Uncle Nick]

the term for the symptom is called "dieseling". this problem only exist in carbureted gasoline engines. the causes could be wrong spark plug heat range, overheating, hot spots in the combustion chambers that simulates spark plug firing or carbon build up in the combustion chambers

Very good suggestions!

But first, check the ignition timing.....it is probably too advanced, for the fuel type, and engine condition.

A higher octane fuel might help, if that is what your engine requires (check the manual).

You might wish to "retard" the ignition timing to protect the engine from damage until you can locate and solve the "real" problem.

Ciao!

Uncle Nick.