All right, ready for something stupid? Took the M out for a test drive to get it up to 40-45. Got up to speed running well then took my foot off the pedal and the throttle did not let up. I reached down and pulled the pedal up, still no decel, so I shut the engine off.
Look under the hood and, long story short, the center stud from the stupid non-stock air cleaner that was on there seems to have fallen down the carb throat. I took the carb, spacer and governor off and couldn't find anything and can't see anything in the intake housing, but I'm pretty sure it's in there.
The symptoms are that as soon as you fire the engine up, it's running at full tilt. I had to crank out the idle screw and choke it severely just to get it home. What's going on here? Why is it getting so much air (or maybe little to no gas) if something's in there?
I'm going to take the manifold off and have a look. I don't think anything is ruined as the engine sounds fine, it's just running at full tilt. Ugh....