KX85 Power valve - sloppy???

Joined
Feb 3, 2005
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#1
I'm into the first top-end rebuild on a "new to us" '05 KX85 and I really wanted to get a good look at the power valve mechanism because the bike seems a little dead compared to our old KX65, maybe because the 85 has a flywheel weight. Anyhow, everything moves easily, maybe too much so. The "butterfly" valve that acts kinda like a little trap door to let the slide valve move forward, sorta hangs down a little and rattles around when it's extended (it pulls up tight when it's retracted). I see no means of adjustment and the tech manual simply states how to assemble and disassemble it. The "chute" that the PV assy slides into seems to be where all the slop originates but it doesn't look like it's wallowed out. I noticed that the head has had some port work done on it, so this obviously isn't the first top end rebuild (couldn't tell by the air filter and silencer though).
At any rate, it looks to me like the power valve makes the exhaust port about two millimeters shorter when it's extended. Does that really have much effect on low end power?
Is a rattly loose power valve assy normal? If not is there anything that can be done to tighten it up?
 
Joined
Sep 12, 2006
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Pro Circuit has just come out with replacement power valves that are suppose to fit better and seal up better than the stock units. I have not used them and only heard about them yesterday while on the phone with a Pro Circuit tech inquiring about one of their pipes.
 
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