I'll defer to Ron's wisdom on this, but I can't help but wonder about the plug your using. I know you said it was a werks plug, but what temp range is it and how old is it? I'm wondering if the fuel isn't completely burning off when you stop the motor. You had said that you're using the flywheel method to stop it, as opposed to pinching the fuel line or smothering the stinger. I would think that with a weaker plug that would leave some fuel behind, that coupled with the local temps not beeing blazinly hot in recent days.