'90 YZ 250 Power Valve Nightmare


Jersey420

Member
Apr 24, 2003
24
0
Got this 90 yz 250 a few months ago, nice shape for a 90, anyway... just had the cyl. bored + honed and the head repaired, new top end, bottoms still tight... My powervalve (both halves) seem to hang up and not operate freely (It's the rotary type PowerValve that Yamahe used for years, some of you guys probably can picture it... and when I put the jug on and went to hook up the actuator assembly, the tension from that little spring doesnt seem to be enough to move the powervalve...
Both powervalve halves appear to have been ground by someone who didnt know **** about ****, do i need a whole new powervalve or maybe get these machined a little to move freely?? \
Any input is greatly appreciated, THANKS! -alex
 

Rcannon

~SPONSOR~
Nov 17, 2001
1,886
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Is the P/V not moving freely because it is hitting the piston? Does the rod that goes down into the case move properly? It should feel quite stiff to "pull up on " but return on its own.
 

Jersey420

Member
Apr 24, 2003
24
0
The power valve is not hitting the piston, i was sure to check on that because i heard its a prob. with these bikes. It looks like the amateur grind job done on the valves was to prevent this... The actuator rod works like it should, i can pull it up and it returns on its own...

There are two issues right now, the fact that the power valve is binding up and the way the actuator attaches, I have everything on as per service manual but that spring isnt enough to move the power valve when I have everything together and try to move it manually.
 

Rcannon

~SPONSOR~
Nov 17, 2001
1,886
0
Is there any carbon build-up on the PVor where it rides in the cylinder? When I first bought my YZ 250, this was a problem. Whe clean and assembeled properly, it returns fairly easily.

How about the "bushings" the p/v caps have? Are they clean?
 

Jersey420

Member
Apr 24, 2003
24
0
Yeah, everything's clean since i just overhauled it. Replaced two of the seals in the power valve on the right hand half, one o-ring came with my gasket kit and i bought the other from yamaha. I'm thinking I'm gonna take it to the machine shop that did my bore+hone and see what they think, maybe they could do something to the valves to make em move freely. I can get them to move fine but then when i button everything up and put the jug on the thing binds. argh.

thanks for the replies!
Good thing i got 2 250's, even though NJ's a big mud pit at the moment.
-alex
 

Rcannon

~SPONSOR~
Nov 17, 2001
1,886
0
It sounds like a missing spacer or bushing. Maybe the previous owner drop kicked it? When the covers go on, it gets too tight.
 

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