Clutch Clutch not engaging all of a sudden?

[quaternium]

I have a two-stroke China girl 49cc. Suddenly, while riding, I had loss of power to the drive and a high engine rev, and pedaling was EASY / not the usual tension I'm used to with clutch engaged. I took off the clutch cover and noticed the large screw holding the small bevel wheel is loose. Could that be it? I'm not even sure if this is a clutch problem. The clutch handle moves the clutch plate as I assume it should.
Bear with me, please, as I'm entirely new to working on these motors (or any motors)

 

[quaternium]

Would this be considered a total compression loss? Clutch slipping? I'm not sure if I should/have to tighten the screw holding the small bevel wheel? Or start messing with the clutch plate and flower nut. Woodruff key? I'm lost.
Like I said, the large screw holding the small bevel wheel gear was loose. Now, I tried to tighten if and it wouldn't. Removed the bevel wheel and it looks like the woodruff key is missing.

 

[Purple Haze]

It sounds like the small drive gear has loosened, causing the woodruff key to come out. Common problem. If you're lucky enough to find the key, use locktite on the screw, that should fix it.