Hi

Typically when an engine does not shut off at idle, you have an air leak. This could be either at the carburettor base or the back plate.

If you can not seal the engine by tightening screws or replacing the carburettor "O" ring, you will have to smear a light amount of RTV (or other silicone high temperature sealant available from automotive stores) on the mating surfaces of the carburettor "O" ring, carburettor mounting base or the back plate, reinstall the components and let sit overnight.

Hope this helps.

Fly4Fun,

Wayne Miller