[Fast Corners]

There are a few different types of "pop off" valves. The most common is a black flapper valve that is installed on the left side of the airbox under the air filter. It looks like a tiny toilet seat. This valve protects the box from cracking when the engine backfires through the intake. If you do not have the valve check the box for cracks and if you have no cracks...install a pop off valve.

Do not let an air cooled motor idle for extended periods of time. I believe that the owners manual covers this issue. From the sounds of it I would believe that you have either a fuel delivery problem or you are drawing false air into the system. Check the rubber boots on the intake runners and you fuel delivery system.