Matt,

We haven't seen this behavior in any of our testing. I would look into the following:

1. If you remove your on/off ignition switch from the battery/ignition loop (i.e. just plug directly into the battery pack) does this solve the problem? If it does, replace your switch. if not:

2. Pull your spark plug and see if you have an accumulation of carbon on the plug. The carbon might be retaining enough heat that the engine continues to run in a compression mode (ala a glow engine.) Clean any accumulated carbon from the plug and retry to see if this solves the problem. If there is an accumulation of carbon this is a good indicator you are running the engine a bit too rich.

Pete