YZ250 with Olin 360 Kit

Hey Guys, was wondering if you could take a look at this picture (attached) and tell me if this is an adjustable item.  I picked up the bike for a measly $100 off eBay a while back and finally got around to fixing it up.  I've put about $400 into not including what I paid for it.  It's previous owners really didn't take care of it.  For example, instead of changing out the impeller, they added radiator gunk which seeped into the crankcase and basically cooked on into the gear box making a real mess.  Got that cleaned out.  Didn't worry to much about the carb because I wanted to test if out in open desert first but noticed at high speeds it would bog down first 1/4 throttle before the engine would start to rev up again list it wasn't getting any gas.  When I got it home and checked the carb, saw the throttle needle clip position all the way to the lowest setting (which would actually raise the needle up so it would seem that wouldn't deprive the engine of fuel when I turned the throttle 1/4 way)  Any ideas what might be causing this first 1/4 throttle hiccup?  In the picture I'm pointing the power valve actuator "lever" which has about an 1/8 in play (up and down) before anything engages.  Is that normal?  I know from reading on the net that the only adjustment (at least this is the only thing I could find about it) was changing the actuator spring which of course is in the crankcase, but what about this bolt I'm pointing to in the picture.  I can't find anything online that says anything about making the adjustment there.  Any help would be great as being old school, you'll never hear me boasting about how much I know about power valves or even 4 strokers for that matter.  This is actually my first water cooled bike and I really love riding it.  Easy to handle, and puts out a really good power band after a quarter throttle. Any help would be really appreciated.  Other pic is of the entire bike.  Getting it ready for my next ride and making some final adjustments here and there.  Can't tell you how many bolts got lose after the restore job from either not using lock tight (which I was trying to avoid) or using a flat washer as opposed to a lock washer.



No mention of the year or model

You can get all your questions answered in the factory service manual, which you should read before attempting to make any adjustments.

Hey Krannie, thanks for the reply. The bike is a 1989 YZ250 with an OLIN 360CC Kit on it. The problem is there is no manual for the 360 kit nor do I have a manual for the 89 250. The part that I am pointing at is the OLIN cylinder so don't know if the 89 manual if I manage to find one will even cover this after market. There is about 1/8 inch play up and down before you feel anything engaging, and basically when I tore it down to do the restore, I just put it back together the way I had taken it apart (I take a lot of pictures of everything I dismantle so when I put it back together there isn't any questions) but when I had taken it apart, I didn't check this 1/8 play so not sure if it's a new thing or something that already existed. From what I've read throughout the net, the only type of adjustment on power valve are just in the actuator spring, but that's not really what I'm referring to. There is no doubt this adjustment I'm pointing at has some significance as to play and adjustment and need to find any info I can on it. The way it is now it doesn't seem to effect performance, at least not from a 1/4 throttle up. The first 1/4 when the bike is in motion just bogs down, but once after the 1/4 throttle position, it powers up again. I did find that the needle jet clip was placed on the lowest position bringing up the needed, but couldn't figure out how that would bog it down first 1/4 throttle. I put the clip in middle like most are but haven't finished servicing the bike yet to check if the problem of 1/4 is still there. Any help on the adjustment of this level I'm pointing on would be super. Thanks

the power valve engages based on rpm, it's centrifugally operated (spins fast enough to compress actuator springs), it increases the area of the exhaust passage. So the bike has good low end and high end, spreading the power and reducing the hit. All the yz's i've owned have had some play on the power valve arm you are pointing to. ie that vertical arm can move up and down a little.


First quarter hesitation would be air screw/pilot territory, right? It won't be the power valve, unless it was frozen open. Edit: Clip position would play late into the first quarter throttle opening.

Edited by Die_trying

Hey DT,

Thanks for the input. Glad to know I don't have to mess around with this. I've suspected the carburation, specially when I tore it apart and found the throttle needle clip on the lowest position. Most I've encountered are always in the middle position. The first 1/4 throttle works fine at idle and at take offs. For example, I'll ride down a dirt road and get my speed up to say 40-50 and let off the throttle, as the bike is still at that speed, I'll start to open up the throttle and as I do, you can hear the first 1/4 throttle bogging down the engine, once you pass the 1/4 throttle position, the engine starts to get power and picks up again. If you come to a dead stop then give it gas it's not problem. It's only when the bike is in motion and going fast enough. It almost seems like when this happens, the bike is flooding or just not getting gas, it just bogs like the 1/4 throttle doesn't work. The bike has plenty of power at take off. The 1/4 throttle does sputter a little, but it doesn't sound like it's dying out like when you're already going 40 and you give it that 1st 1/4. I moved the clip up to the middle position but haven't tried it yet because I had concerns about the power valve. But you've answered my question there, so I'll discount that and just fire it up again and see if the throttle needle clip position was the problem. I'll keep the post active once I've put it all back together and given it a try.

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