03/YZ450 Jetting for 110 octane.

I'm using 110 octane.

I've noticed some chop at full-throttle and a little backfire during deceleration.

The plug looks clean and dry, whitish brown.

Jetting = all stock, main jet 165, jet needle clip pos 4, pilot air 1 1/2 turns.

Does the backfire indicate rich or lean?

Any suggestions?

Sounds like you're a bit lean. Have you done any mods to increase the airfow; removing airbox lid and exhaust restrictor? What's your elevation?

You're overkill on the octane and will get no benefit from it. It burns slower which may cause deceleration backfiring, besides being lean on pilot.

I have an 03 WR250 and I run 110 octane as well and experience the same problems. Everything else is great. My plug looks brand new all the time.

Thanks for the suggestion.

My dealer reccommended race gas for cleanliness, 110 is the only race gas I can find around here.

I installed a 170 main jet and dropped the needle jet clip down to position #5.

The popping and the back-fire is gone. She runs like a raped ape. :)

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