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thmlrmg

08 yz450f jetting

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Hey guys I just have a quick question. I just bought an 08 450f and I was wondering about jetting. It is quite cold here (in the 20's) in tennessee and I have noticed that the bike runs lean in the cold and the header pipe glows red real fast like under a minute. When the temps were in the 60's it would take minutes for the header to glow. My question is how big of a jetting adjustment should I make when the weather hovers in the 30's?

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Roughly,...

you should increase the jet size by 2% for each 15-20 degrees dropped. So, from 60 to 30, you should go 4%, which is from a 160 to a 165, and a 45 to a 47 (or a 48).

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Once the temps dropped here I went to a 48 pj, no change to the main or needle clip position and the bike runs good.

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