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YZ450 Factory 4 Jetting

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I have a 04 YZ450 all stock except for a FMF Factory 4 exhaust I just installed. It ran pretty good before i installed it and now it kind of cuts out a little in the mid, but pulls hard on top. Tried the FMF Jet kit in all sorts of different ways and said screw that and then went back to the stock needle. Just wondering if any of you guys are running this exhaust setup at about 4,000-6,000' and if you would give me a hand.

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Getting rid of the Dynojet kit is your smartest move, as I have not found much use for them. As many people on this forum will tell you, getting the JD kit for your bike will probably help in a big way, but if you decide to stick with the stock setup, I can tell you that I tried every different combination, and always went back to the same setting. On my '04, with factory 4, I run a 42 (stock) pilot, 168 (stock) main, clip on the 3rd (one leaner), fuel screw at 1 1/2 turns, and my bike runs clean throughout the powerband. I am at 3500 feet, temps lately 90 - 100. This has been the best setup I've found for my conditions yet.

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The cutting out in the middle is probably a rich condition. Use a leaner clip position (as suggested) and/or a leaner main jet by 1 step.

A lean condition would more likely just feel weak, but not cut out.

James

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