2008 rm250 jetting issues

daveep1983
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Toms River, NJ, USA
daveep1983
Hi all i have a 2008 rm250.... new motor nickel plated cylinder... rad valve... fmf fatty with powecore2 silencer... running vp fuels t2 40:1

Bike was running as good as it ever could around 50° f i switched to the race gas and threw in a iridium plug and seemed to be running a touch lean...

Now its colder around 30-40°f and the bike wont run at all.... its starts right up no problem idles and revs just fine... as soon as you get on it to ride it straight up dies at about 1/8 - 1/4 throttle like im hittin the kill switch...

Im guessing im running lean and now with the cold air its just way to lean and wont run?? Anyone have any other ideas??

Any suggestions would be greatly appreciated... i dont know what jets it has but im assuming stock jets...new plug was lil white but didnt really do the riding to get a good reading... previous plug was a perfect milky brown before race gas / iridium plug and temp drop....


Im gonna grab a jd jet kit hopefully tomorrow and call jd fmf and boyesen to get their recommendations .. im guessing my needle and clip position need to be changed and prolly the main jet??

any help/recomendations here would be greatly appreciated

PLEASE GIVE INPUT AND HEEEELP ME 😁
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Paul_Pitzonka
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Paul_Pitzonka 12/20/2020 5:34pm
12/20/2020 5:34pm Edited Date/Time 12/20/2020 5:36pm
T2 is an oxygenated fuel (spec sheet states 5.94%)... My understanding is by theory this means you should start with a base jetting that is at minimum 5.94% larger than your current jetting. (this is also assuming your prior jetting was correct)... The oxygen content of the new fuel combined with the increase in air density (drop in temp) has more than likely caused a lean condition... ***Side note*** Something to always remember When making jetting changes to accommodate for a fuel change is it’s always better to start on the rich side!
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