Re: lost power
from the description it *sounds* like a gasket problem - if by screws on the side you mean on the cylinder or the side plate on the crank.
Two strokes use the crankcase as a pressurized part of the fuel system - if pressure is lost or reduced then the engine will not run as well..
I would suggest having the head and cylinder off the motor and checking the gaskets for leaks - that will show up fairly readily.
there might also be a problem with a broken ring or circlip as well, although I find it a little strange in both cases that you would have been idling when it had this problem..
hope that helped...
"....Look, no pedals... *thud*..." The mating call of the motorized-biker.
"RetroEagle" - 32cc Two-Stroke, Piped. 35mph on #13 gear. Reversed stem with springer fork.