Occasional Flame out

I ride an 09 YZ450 with an R&D Powerbowl and Remote Fuel Screw. I have also added a JD jetting kit. I must admit the bike went from barely ridable to an absolute joy.

The problem I'm having which I guess isn't even a real problem is that occasionally it will flame out on the 2nd or 3rd blip of the throttle in the woods. Certainly not something it would encounter on an MX track but we ride some real tight woods here in South Carolina. James Dean of R&D recommended using a #52 pilot jet. I respect his knowledge totally but I would like some input from someone around the Southeast as to what they are using to try and eliminate as much testing as possible. It currently has the stock #45 in the carb and is a little too crisp off the bottom for woods use.

Has anyone solved this problem in the Southeast? If not I will surely try his recommended #52 but it just seems like a big jump to me.


The most likely cause, if I read this right, is that you have too much AP squirt, and/or too small a leak jet, and/or too rich a pilot. This kind of thing leads directly to the symptoms you mention as I understand them.

What gray said your leak jet screw needs to be tured in. I have the same bowl.

Sounds good I'll try to turn in the leak jet screw.

Thanks again for all the help.


If turning in the leak jet screw makes the leak jet smaller, I'd say that was the wrong way to go.

gray i think your right sorry ill keep my yap shut.

Edited by s14 2510s

It's funny. I took my 09 450 out for the first time yesterday (riding desert) and was experiencing the same thing-2 or 3 throttle blips and the engine would die. I was thinking all day that I would have to come on here and do some research. It's nice the help I needed was on the first page:thumbsup:. The bike is also SUPER touchy at low throttle openings. I guess this would add to the evidence that the ap is squirting too much fuel.

Now I was under the impression throttle crack type stalling were from a too lean pilot and or air screw condition ? Sounds like the generall opinion is the original poster's low speed circut is too rich ? He's claiming he has the stock pilot jet, and in my experiences, the stock pilot is too lean in all but 80F+ temps

The OP states the stall occurs after 2-4 blips of the throttle, which suggests to me an accumulation of fuel resulting from too much AP delivery "loading up" the engine, which then stalls at the closing of throttle on the final "blip". I could be reading this wrong, but I kind of doubt it.

Just as a lean idle causes the engine speed to "hang", or return to idle RPM slowly, a rich idle causes the idle to drop off too quickly on a throttle chop, and commonly results in a tendency to stall at low speed. Given the tendency for people to worry excessively about any trace of decel backfire, and to chase the complete elimination of any sort of accel bog, even when snapping from idle to WOT as fast as physically possible, I see one bike after another that runs too rich at an idle, dumps way too much fuel though the AP, and/or has such a small leak jet passage that the smallest turn of the throttle washes the engine with gas.

It's too bad that the manufacturers of some of the high priced gadgets available to "correct" the "problems" with a YZF carb keep encouraging unrealistic expectations and the desire for the "easy solution".

Gray thanks for the input and feedback, I want you to know I appreciate you as well as the rest of this forum community who have shared so much.

I was still having problems with my bike not returning to a normal idle but also the flame out which seems counter intuitive. But I made few discoveries today while riding in one of our national forest OHV areas.

First the return to normal idle has to be some sort of mechanical thing. I met a guy with and 07 450 and noticed his bike was idling much lower than mine, monkey see monkey do as it were, so I lowered my idle and miracle of miracles it snapped back to idle everytime.

The second was that adjustment of the leak jet really did solve my flameout problem. I'm not sure if I ended up with it turned farther in or farther out because I wa adjusting it and blipping the throttle. So, no technical help there but it worked. The bike was awesome, the rider mediocre. Those magazine guys who said this bike won't turn must be infinitely better than me because I cutting through the trees faster than I ever have and the front end was never a thought while doing so. If I don't have to think about it when I'm slicing and dicing then that means it works....


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