popin n boggin

[PGH PA 2 STROKE]

my 1993 RM125 engin on my quad is popin and spitin real bad shootin sparks out
the pipe and when its at more then 1/2 throttle it boggs down but at less it will red line with no prob at all whats goin on here? .... its great on a quad good power and speed ... its for sale too i need cash for my good blaster

 

[Awk08]

poppin usually points to firing at the wrong time????
check the woodruff key in the flywheel, may have sheared