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Fresh 426 motor not starting easy

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The bike engine has finally been rebuilt. I’m finally back to riding, and need some advice with its setup. Before I ignorantly ignored my cam chain stretching the bike was running great. The throttle response was strong from the bottom to the top with no hesitation. I credited the response to the power now, installed to get back some of the bottom end grunt lost with the YZ 450 EX cam.


I made the assumption that if I left my carburetor alone and simply put it back on a fresh motor. The beast would be back. She has the dreaded hesitation off of the bottom and doesn’t want to start. Bumping the pilot up and installing the O ring mod cleaned up some of the hesitation, but was awful to start unless I turn up the idle high.


What can I do for the starting problem? “Will start with a slightly cracked throttle”

O ring mod in conjunction with the BK mod? “recently installed the O ring mod”

I have RedBeard450’s AP Mod How to Guide and this doesn’t look like a fully applicable mod to my 426.

Will the carb need a little tweaking once the motor breaks in.

02 WR426

160 MAIN


Skinny YZ needle “I would have to pull for number”

CLIP # 2




Grey cut / Yz throttle stop / Uncorked / O RING MOD / BK MOD / POWER NOW / HOT CAM EX (for the decompression ) sea level to 1000’

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