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jetting ?

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I have an 05 yz250 I can't seem to get it jetted. It seems rich I am running sunoco 110 race gas 32:1 yamalube 168 main stock needle in 2nd clip pos with a 48 pilot it has a rad valve on it to. It still seems rich. I have checked the power valve and put a new pro circuit silencer on. My elevation is sealevel to 1000' I have jetted a lot of bikes and I can't get this one. It just does not run right I don't think. When you hear it run it sounds loaded up. My buddies 2001 kx250 sounds crisp and runs great same gas as I use but he runs his 50:1 and stock jetting on the kx.

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The Rad valve is a real pain to jet with. I never bothered with it on my new yz, but I had to go EXTREMELY lean on my old YZ. Far larger steps than you have gone with your machine. I often described these as a "300.00 investment" 150 for the valve, 150 for the jets.

I would go leaner yet, or drop kick the rad valve.

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Before I put in the rad valve I had the same thing going on. I have not checked the compression on the bike but if feels like it is good. My next step is to rebuild it and start from there. Did you have to go leaner on the pilot and needle as well as the main?

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I think I will try a 45 pilot. My air screw is out 2 to 3 turns out with the 48 that is where it seems the best with the 48.

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To get any benefit I had to go leaner across the board. Pilot, needle and main.

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I run the ProCircuit jetting spec with good results (175mj 48pj N3EW #2 1.0as). The bike does load up a bit when run at low rpms for a while (it is a race bike after all), just hold the throttle WFO a few times until it cleans up.

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I can ride tight, tight single track lugging just off idle in 2nd or 3rd and not load up; it's not the fact that it's a race bike, it's jetting.

I run Sunoco 110 40/60 w/pump 93, Yamalube @ 32:1 jetted 175 main, 45 pilot, N3EJ 2nd clip, air screw 2.5 turns out @ sea level. This is with the pipe spacer, Bel-Ray filter oil on the Twin Air AND Filterskin. All else stock.

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I'm using Vforce3 and I'm all the way down to 42 with the pilot and 162 main. The 42 still seems too fat. The needle is next on my list for tinkering as the throttle hangs a bit. Just be prepared to go leaner than normal.

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Sea level, have a Rad valve main jet 175, 50 pilot, 2nd clip from top on needle. U.k bike so mainly damp cold and miserable weather with brief interludes of nice stuff. Any smaller pilot and it goes super lean and rev hangs(was the same with the VF3).

Went from V-force 3 to rad valve and dropped the main jet from a 178. Runs superb, can't really say if it is much better than the VF3 but am in no hurry to swop it back. I only use pump gas but get no pinking or muck out of the tail pipe so prettty happy. Have you given the carb a good clean and treated her to a fresh spark plug. Might be worth doing before the rebuild.

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Try mixing the Sunoco 110 50/50 with 93 pump.

The 110 is overkill and a slower burning fuel than the 93. What isn't burned goes out the exhaust port. Just a thought and easy enough to try.

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The 110 is overkill and a slower burning fuel than the 93...

The octane rating alone won't tell you anything about its flame speed. It is simply a number that relates the fuel's ability to resist combustion under a certain amount of heat/pressure, and nothing more.

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