1991 KX 250 Power Valve

Okay, so its a 1991. 


The power valve is not operating. Yet, when you take the little brass ring off the power valve rod you can pull the lever sticking out of the case that actuates the power valve and it snaps back as though it is operational. Also you can pull the power valve rod sticking out of the head and slide if back and forth with ease. We've also confirmed the the power valve itself is working as when the bike is idling you can slide the rod in and out of the head and the power valve opens and closes.


very confused as to why the power valve actuator in the case cover does not actuate and open the power valve when everything is hooked up. We've check the manual and all.


Any thoughts?


To me it seems as though the power valve spring is wayyyyy to strong and just isn't letting it open?   

Pull the side cover off and take a look.  Springs don't get stronger with age.  Two things that come to mind are the drive gear and the little ball bearings that drive the actuator.  Some older bikes had a plastic drive gear which can disintegrate.  Its also possible that someone screwed with the actuator and lost some of the little ball bearings.  Without all four in place that thing isn't going to work.

Hey Dan, I should have mentioned that part, it does have the plastic gear but it's in really good shape, and all 4 ball bearings are there. Any ideas?

Don't know what to suggest.  Have you taken the pipe off and looked in the port to ensure it goes through the full range of travel when actuating the valve by hand?

Oh yeah, it's got full range of travel. We actually did a quick hack to keep it open. Took the plastic cover off, removed the outer circlip holding the little brass cheerio on and used a zip tie to hold the power valve rod in the open position while running and the power valve is certainly operational. It's got something to do with the actuator with the spring and ball bearings. Just dunno why it doesn't work... We've looked at the exploded view of the whole actuator and confirmed all the parts are there in the right order as well.

So if the power valve itself is functional that would mean that the actuator would be the issue? I will take some photos to post

Its possible the actuator is stuck.  Might be a piece of debris or something in there.  Every one I've ever taken apart used a pin through either end of the center shaft.  They come apart pretty easy. 


Is it possible you're not getting the actuator connected to the linkage arm when you put the case on?  You usually have to place the KIPS actuator into the side case to make sure its engaging the linkage and then install the side case with the KIPS actuator in place onto the engine.

That's the thing, we've had it apart and back together a few times, everything looks good and we hold it in the case cover with the linkage when putting the cover back on the engine. It's driving me nuts haha

There must be something going on.  Have you had the cylinder off and cleaned the power valve?  They can stick if you've got carbon build up in there.

It was all apart last Saturday, the power valve assembly in the cylinder functions perfectly. I previously mentioned out redneck zip tie trick to hold the power valve open, well we took it for a ride and it's definitely open haha. It's not sticky or stuck at all

And you can actually grab the linkage sticking out of the case cover and pull it away while not attached to the power valve rod and when you let it go it snaps back in. Haven't pulled on it while it's running though

The photos show the power valve opening and closing and that the linkage moves back and forth as well.

Link to a video with it running and manually opening and closing the power valve and moving the linkage. It snaps to the closed position quite hard.






Edited by d3kubicek

Allow me to ask a stupid question but you do have the collar and circlip that connect the arm to the KIPS rod right?  I'm guessing you took them off for the picture? 


Have you tried revving the engine up with that cover off to see if you have any movement?  You have to rev it pretty high to get that actuator to throw.  Much higher than it is in the video.

Edited by turbo dan

Haha yeah the brass cheerio and circlip are off for the photos and video. And I've when it was together I road it wide open from first to fifth. Also left it on the stand with the cover off the mechanism and revved the hell out of it and it doesn't move.

Next step would be to order a replacement actuator on ebay.

I was just looking on eBay lol thanks for your insight Dan

Looks like 90-92 are interchangeable...

I'm late to the game here, and I might have missed this point. But did you test the governor to see if it's opening and closing? Im not sure about your year, but there may be flat spots machined at the top of the actuator shaft (name? The shaft coming out of the case) for a spanner/wrench. With the wrench (not easy by hand) you can turn the shaft and test the spring. And on my 100, I can see the governor very clearly through the oil fill hole.

Just went through this. Mine was seized open. But Dan already knew that :)

Edited by Bron-Yr-Aur

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