My 86 kdx200 is acting very funny on me. I know it needs a top end as there is little compression but when I start it up it idles ok. I ride it around for a few min and all of a sudden the pegs its self and sounds like it is just going to tear its self apart. I can be completly off the gass just ideling around in 1 first gear and the thing will just want to take off when it goes full throttle. I have to stand on the rear brake to keep it in control. It is actually quite scary. Any ideas?

Slide could be worn or dirt in the carb. Throttle cable could be fraying. Needle could be jacked.
Just take apart the carb and make sure everything in there and your throttle cable is good

yea sounds like a needle and slide sticky issue to me as well

check your reeds.

i've never experienced it but have been told by a mechanic i know.
he said that when your reeds break the motors somtimes do nothing but a perfect idle and a top end you never thought possible.

i don't know if it is true but they are easy enough to check. especially if you are going to pull your carb. and if the top end is tired chances are that your reeds are too.