426 stalls right off the line

My '02 YZ426 has developed a stall right as you blip the throttle. The engine is aleady up to operating temp and it's usually when I pause for other bikes to catch up on the trail. I blip it a time or two and before I even grab the clutch and it dies, I have to hot-start and there goes my lead. I've had the carb apart recently so I don't think it's trash in there but I can't figure what else. It's actually done this from the start but a lot more recently so mabey it's a jetting issue?

Does the accelerator pump work? The pump shaft may be stuck, or the check valves or diaphragm leaking.

I've not been into the carb that far, just cleaned out the pilot jet cause it's been collecting grit lately.

What should I look for in the way of a stuck pump shaft or damaged diaphragm?

Either remove the air filter, or the air boot, and look to see if the pump actually squirts fuel.

The shaft is on the right side of the carb under the throttle cam cover. It should move as the throttle is opened and closed. They have been known to gather dirt around the point where they enter the pump housing and jamb themselves.

Either remove the air filter, or the air boot, and look to see if the pump actually squirts fuel.

Do this with the bike running or not?

Not running. Not too many times, either, if it pumps. You need to look into the mouth of the carb for a stream of gas being sprayed up and into the throat as the throttle is opened.

Would you recommend replacing and/or upgrading the pump on a bike this old with a lot of hours anyway? I've recently replaced the boot on either side of the carb along with their o-rings recently because dirt kept getting into the pilot jet, but didn't concider reworking the a-pump at the time.

If the diaphragm looks cracked or tired, I'd replace it. I don't think it needs to be upgraded beyond the BK Mod

Thanks :thumbsup:

I just cleaned my entire carb this weekend. Not much too it. Mine had a bunch of crud in it and was bogging, stalling, and basically running like crap. The carb should last much longer if you clean it out.

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