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Is this a jetting issue?

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TIA for responses.

I purchased a '00 YZ250 this spring and it ran strong for the first 3-4 rides. Top and bottom were supposedly redone w/about 10hrs of break-in before I purchased it. The last couple of rides I have lost all power at my middle-to-top end, it simply isn't there. The bike just "flattens off and I have to shift up. I have pulled the plug after the last 2 rides to find my plug black and oily (running rich?). I pulled my main and pilot jets assuming that my main jet was rich. The stock settings on my bike are as follows: MJ - 175 (actual was a 170), PJ - 50 (actual was a 48), needle - position 3 (actual was position 1 'clip all the way at top').

From what I found it appears that both jets and my needle are set lean.

I will qualify this post by saying that this is my first bike and although I've spent hours on the forums, I'm not sure my basic understanding of carbs is correct. Again, I appreciate any help all you experts out there can offer.

Dave

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I am having the same problem with my 00 yz250 , anyone know where I can buy a jetting kit with a bunch of different needles?

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Have you cleaned your air filter lately? Dirty filter will drop power big time, or If you have cleaned it, did you over oil it?

Also check your compression, it may have worn the rings abit from being too lean, and now you are getting oil blow by from below, hense the black plug.

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Power valve sticking shut? If the power valve isn't functioning correctly it will either have good bottom with no mid/top or it will have no bottom with good mid/top. Sounds like it may be stuck closed.

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Top end power is dune by the main jet. im having the same problume right now too.

does yours pop alot if you give it full throtol?

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Thanks for the great responses. Sounds like I've got a few things to check.

cj-S4: I just cleaned and oiled my air filter (hopefully not too much). I don't believe this is causing the problem. I pulled my reeds and they are black. Is this caused by blow-by? I will check my compression.

Baron & James_Dean: Sounds like I'll also be checking my power valves.

5star: I have not had a problem with popping. Power simply goes "flat".

Dave

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When looking at the reeds, you want to look for cracks and see if they are sealing against the reed block. It sounds like you may need to do a top end sometime soon though. The previous owner may have been FOS about recently doing it.

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i kinda of had the same problem with my cr125 i was running to lean of a oil at 32:1 , when i went to a 40:1 or 45:1 it got alot better.

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