Inliners International Forums General Discussion Engines engine backfire/hissing ?

It sounds like the engine might be dieseling.You may have the idle speed set to high and have carbon deposits built up in the head.You might want to check your idle speed and add a anti diesel solinoid.A water injector will get rid of the carbon deposits.Amsoil makes a product called Powerfoam that also will get rid of the carbon deposits.
EvilDr235