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Backfiring/wont run crf 450 stroker HELP!

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Hey all, I just finished rebuilding my 2006 CRF 450R. I installed a 3mm stroker crank, 13.5:1 JE piston, and faction mx intake and exhaust valves (also had my seats cut). I just got everything bolted up and.. Yikes! I finally (after 10 min of kicking) got it started. I started it up, warming it up with the choke on. as soon as i turned off the choke, when i rev it up it pops and backfires horribly! and wont idle and just flames out and dies. I need some help! Also, no matter what I do with the fuel screw it does not change it. Thanks!

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Forgot to add, It ran really well with the choke on. I ran it up and down the road with the choke on, and it ran great.

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Its lean!! Check your hotstart at the carb and make sure its not stuck or leaking etc. Im sure youll have to rejet for the mods as well. And maybe a clogged idle ciruit?

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Well guys, it was the "dreaded floating slide plate". switched that around, started right up. she runs like a boss! It runs really well with the jetting the way it was before i put in the 13.5:1 piston and +3mm stroker crank. It runs great with the same jetting. Should I mess with my jets to perhaps gain a little power? Thanks guys!

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