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08 crf450r dieing stalling loss of power

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I recently rebuilt this engine with new cases, gaskets, seals, ss intake valves, new springs, timing chain etc etc etc...

It ran awesome for about 4 hours or so. On my last ride on the way home in probably 4th or 5th gear with partial throttle the bike seemed to bog down/stall for just a moment like a split second. Almost like it would stop getting spark for just a split second then keep going. This happened over the course of a couple miles. I'm not 100% sure but I think increased throttle did stop this from happening.

Before this ride I did mess with the air screw on the carb, could this have caused this behavior? potentially a mix of the intake valves being at .009" and me not setting the air screw correctly?

I am in the process of re-shimming the the new intake valves and replacing a few odds and ends to make this bike 100% so before I order anything I thought I would post here and see if anyone has any experience with this. Thanks in advance for any input.

20170522_154612.jpg

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Running lean.
4 strokes don't have air screws, they're fuel screws.
Check idle screw adjust and ride for a while.
Also there's an air jet on the carb face (airboot out).
Make sure it's clean.
Buy Eric Gore's book "the CRF performance handbook".
Jet fatter.

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Also check for shorts in wiring and anywhere the ignition/CDI could touch ground.
Usually stuff that dies on trail is something that moved or got damaged during the ride.

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Great info guys. Thanks for the help. When I get it shimmed and back together I will look into all the stuff mentioned.

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Just reading the title had me thinking the bike was lean and overheating. That plug is absolute confirmation.

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Definitely way to lean, Did the bike sound like it was surging at all? Also in 4th and 5th gear what percentage throttle would you say you had it pinned at?

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