Stalling issue

So I've been fighting this problem since I bought this bike about 6 months ago and I'm running out of ideas. My bike stalls at idle at times and on uphill climbs (I have a Rekluse). It's really frustrating. I've tried every thing short of pulling the carb completely apart. I've replaced the jets, replaced the spark plug, I've tried a few different jetting combinations, and I've installed a heavier flywheel. What's weird is it seems to run lean erratically. I'm running a 48 pilot jet (at about 700' elevation 80-100 degree temps) which should be too rich. It's almost like it has a vacuum leak or something. I've got a Boysen quickshot on it also, but I doubt that's the issue since it doesn't stall when chopping the throttle.

Does anyone have any suggestions on what to look for here?

Edited by RiderX

Hmmm..... :smashpc:

I've had stuff like this happen to some of my bikes in the past. Once, it turned out to be a messed up tank vent valve (those one-way valves, stuck in a hose that comes from your gas cap). It wasn't letting ANY air in as the fuel got used. Took me awhile to figure that one out..... Had the carb apart a couple of times, & etc.....

I'd start with the basics, and then go from there. Check the aforementioned fuel vent, then your tank's petcock screen, the fuel line, and then, as much as I hate to say this, you may need to look deeply into your carb. :busted:

What year & model of bike are you working on here?


In EDIT: Sometimes turning your idle speed up a little (within reason) will help to prevent stalls. Where are you at on your fuel screw adjustment? Does the fuel screw have all it's hardware (the washer, spring, & o-ring) in, and in the correct order? Just thinkin' off the top of mah punkin head here..... :thumbsup: I'm guessing that somewhere, somehow, your fuel supply or your low throttle circuits in your carb need help. After that, would need more info (how many hours, maintenance done, & etc.).

Also, WHEN does it stall on ya? With the throttle closed (braking/slowing situations?)? Or when ya whack the throttle open?

Jimmie (again...)

Edited by Diesel Goober
forgot to mention some stuff.....

I've checked the fuel vent (I removed it to see if anything changed-it didn't), and I recently installed a new WR petcock. The fuel seems to flow fine when I remove the hose and turn the fuel on. I forgot to mention my bike info, lol. 2009 YZ450F, about 50 hours on it. I guess I need to just mess with it until I find the problem. It does seem to only affect the pilot circuit. Today I rode it for about 30 miles, and it rode fine at first. It started stalling as usual after about 10 miles into the ride, so I leaned the fuel screw from 2.5 turns to about 1.5 turns out. It ran fine for a while, then after about another 10 miles it started running like it was really lean (excessive popping on decel) and stalling even more. :smashpc:

Well, I'd probably guess it may be time to open your carb up, and check it for a small "chunk of junk" in one of the little passageways inside it, or dirt in a jet, or ??? Hopefully, that will address the stalling..... :smashpc:

Here's a link to a decent article on how to take apart & clean an FRC MX carb:

Hope this will help ya some!


Nice link, that will definitely help.

When is the last time you checked your valve clearences?

i had a similar issue in the hot weather with my 07. turned out to be the tank vent valve. I now run just a vent hose with no check valve. I also had an aftermarket fuel screw that was not staying tight. fixed that too. between the two no more stalling problems. A friend with a WR450 had same issue and it was his tank vent also.

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