Rode great for two weeks, now odd engine issues

I had my motorized bicycle working great! Was getting me to and from work and then some.

But now, when I peddle up and release the clutch, I here a load squeaking and the engine doesn't even dare to turn over. And it was just working this morning. >_<

I thought I might have been losing engine power over the last few days, but I excused it as "getting used to the speed".

In an attempt to be good and maintain my engine, I removed the head to get some carbon off the piston. First thing I noticed was the gasket was scorched with some frayed metal. I don't know if this was a recent development or weather it happened a month ago when I first got the motor running and accidentally ran it a little hot. Then I raised the piston and tried to get off some of the carbon, but it was caked on pretty good, so I left it for the time being. I went outside to try and fire her up and... nothing but screeching. Took her back in and popped back off the head. The carbon on the piston was now loose? I cleaned off what I could and then reassembled the head, but still no dice -- just a loud screech.

IDK whether or not the engine is pulling in fuel anymore.

Things that have changed since it's worked at it's best:

-Being through my second gallon of fuel, I leaned the mixture from 16:1 to 20:1.
-I removed the cylinder head to de-carbonize the piston.
-I switched to premium fuel.

I'm at a loss, and really need to get to work tonight :/ Any ideas?

Thanks much,
-J

I'll take a look, as I haven't tuned the clutch at all yet.

Also, I noticed it was suddenly easier to push the bike forward with clutch engaged, so maybe there is an air leak around the gasket? The squeek might then be the sound of no fuel and thus no lube in the chamber. Better replace.