bogging between 6-8000 revs

[brettly]

hi all
got a tzr 125rr that bogs down when i try to rev between 6-8000 revs and won't rev out either.
its not restricted as it used to rev to 12000 revs no probs.
any ideas.?
i'm thinking perhaps crank seals but not sure.
thanks
brett

[kasandrich]

Power valve sticking? I know thats what the RS125's do if the power valve sticks.

[Tark]

Does sound like a Powervalve problem. Have you checked the cables and valve moove freely with the cover removed?

[brettly]

hi all,
i disconnected the powervalve from the servo and opened the valve fully open, still bogging down, but after i took the exhaust of i've noticed a lot of black oily crap around the exhaust outlet.
any ideas.
i still think it could be crank seals but i'm no mechanic and the last thing i want to do is drop the engine out to split it.
so any advice as what it could be will be greatly appreciated.
thanks
brett