KDXRIDER.NET

So I was working on my 1985 kdx 200, and was finally able to get it to speed. If you havent seen my other threads, my bike runs pretty bad and isnt to great. But anyway, I rode it for like 5 minutes, and i guess it warmed up and I was magically able to get to higher rpm's. So I was riding, and when I rode downhill, my bike would always stall out unless I gave it more gas. but thats not really related to this post. So while I was riding I was hitting decent rpm's, but nowhere near redline. however, when I put the bike in neutral, I was able to rev it and it hit redline, which was insanely loud and scary. The next time I put it in neutral though, I revved it probably to 3k rpm, and then it randomly jumped to redline, and I wasnt able to stop it by messing with the throttle on the handlebar. I had to killswitch it. What could cause this? My damaged lower cylinder gasket?

I would check for an air leak first.

Replace the bad cylinder base gasket. That would be a source of air leak, which would cause all sorts of performance problems.

damaged lower cylinder gasket??

Partially plugged muffler ???