rm85 exhaust valve: how does it work?

[terrible]

I'm having some problems with my rm85. The bike is stock as far as the motor goes. I've got about 15 tanks of fuel through it on trail rides (no racing if that matters). The problem is an odd sound and a loss of top end power.

I took the bike to a large plot of land with wide open trails and very rocky terrain. I ran the bike wide open a few times across an old air strip while I was there (chasing a 700 twin kaw quad) and shortly after I started hearing an odd sound when I would try to go wide open without slowly opening the throttle.

I have since taken the plug out and it looks great. I started thinking about the exhaust valve and thinking I have yet to clean/service it unlike anything else on the bike (filter, crankcase oil...etc) I did notice when I pulled the cover off of the vavle housing there is quite a bit of oil in there, burnt 2 cycle oil that is.

How exactly does the valve work? What can I look for to see if something is wrong with it?

 

[RM85rider123]

describe the sound? where is it coming from?

EDIT- it's most likely not your exhaust valve. It's probably a chipped reed.

 

[terrible]

Pulled the reeds, everything is kosher there. I have the top end off now and the ring was stuck in the land on the piston. Might have got a little hot but not really sure. I'm going to clean everything and slap it back together. If nothing else I'll try a new plug and then a rebuild on the top end I guess.