Power Valve Question

[bigfabber]

Hi all, newb here. Seems lots of you love tearing your bikes down so I bet can answer this. (checked all the 250 pages, no answer)  I have a 91 KX250 that I am working on for my son to ride. I bought it recently and it has a fresh top and bottom.  The bike has no low end power, but seems to run okay otherwise, with plenty of compression. I thought maybe just out of tune, it had sat awhile. I just took the clutch side apart to repair the kickstart, which is done. While it is apart, I looked at the power valve assembly. I have a parts engine on the bench for comparison.
       The valve parts move freely when the rod is pulled in and out. However, when the rod is held tightly, there is about an eighth of an inch of freeplay in the valves. The parts engine does not have this free-play. I don't know whether the parts engine is just carboned up or if the one I am working on is worn out. Any input would be welcome. It has been a lot of work ( and reading in the manual) for me to get as far as I am. If I have to replace the valves, I have buy some gaskets and pull the jug, a big job for me. Better to do it now, than have to tear it all down again soon. Hope you guys can steer me in the right direction, thought my boy and I would be on the trails together by now.
                                      Dave

[bigfabber]

Come on guys, is there freeplay in powervalve assemblies?

[AwfulSmokey]

Yes, there is free play. How much exactly i couldn't tell you. I just did the power-valve assembly on my KX250.

[bigfabber]

Been ages since I've been here, but thought I'd follow-up since somebody else might read this someday and wonder. The PV assembly that had the slight play in it was the right one to use.  1/8" of play seems fine. There was another PV issue as well. When the head was tightened down, the PV would seize up. Finally found that one of the two aluminum "plugs" that go in on top of the PV assemblies was slightly longer than it should be and it would cause the PV to bind when the head was tightened. The PO had never got decent power out of the bike, this is why. I don't know if it was a part from a different year or what, but after filing the plug down to match the other, the PV moved freely and the bike ran like new. Finally the new crank, piston and pipe can do their thing. We have since had another tear down episode due to a broken water pump gear and resulting hole in the right side case, but all is well now and the bike flies. Too bad my 14 year old son rides it, makes my 91 CR250 feel a little tired now. Looking into a rebuilt 97 KX500 for spring, that should level the playing field a bit.