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Discussion Starter · #1 ·
I have a 2006 WR450F, I did a JD Jetting kit when I got the bike and jetted for above 9,000 and the bike runs great. it's a 45 pilot jet. It took me a while to get the fuel mixture and idle right, i'm about 2 turns out on the fuel screw which seems to be the sweet spot. My question is I notice when coming back from the trails on the road going downhill, when I down shift as the revs come down the bike will backfire once or twice, seems like it's only with fairly moderate engine braking. I've been told it can be bad gas. Unfortunately yes I've been using ethanol containing gas. I've heard jet fuel can solve this problem. Looking for any advice. Thanks in advance!
 

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Backfire is caused by having unburnt gas in the cylinder when the exhaust valve opens. There's likely no problem with your fuel or carb. It's common when giving a constant fuel supply and then downshifting to force the rpm to rev. That basically loads the cylinder and forces the exhaust valve open while the gas is igniting. Adjusting the valves will help fix the problem.
 

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Discussion Starter · #4 ·
Backfire is caused by having unburnt gas in the cylinder when the exhaust valve opens. There's likely no problem with your fuel or carb. It's common when giving a constant fuel supply and then downshifting to force the rpm to rev. That basically loads the cylinder and forces the exhaust valve open while the gas is igniting. Adjusting the valves will help fix the problem.
Thanks for the reply! Yes otherwise the bike runs great and has loads of power
 

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If it runs good besides that, I'd leave it alone until your next major service. If it gets worse, i'd get the valves adjusted. Something else to try is using the clutch when you down shift, but that gets annoying IMO.
 

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If it runs good besides that, I'd leave it alone until your next major service. If it gets worse, i'd get the valves adjusted. Something else to try is using the clutch when you down shift, but that gets annoying IMO.
I always use the clutch when downshifting. The backfiring happens as the RPMs settle, if that makes sense.. I'll get one loud pop.
 
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