2000 YZ 426 Idle Issues / Popping

I just bough this bike the other day in a not running great condition. It has a white brothers e-series pipe (5 discs), remote hot start lever, 2-stage air filter, and is jetted with the stock jets. The weird thing is that the guy told me it was jetted for higher altitude (3000’), and I am at sea level, but the jets are stock. Should they be richer for sea level with this pipe and a 2-stage air filter?

My problem is that when I start it with the fuel screw at about 2 turns out it will idle really high with the choke on and not at all with the choke off. The whole time popping while it runs. The RPMs go up and down randomly while I hold the throttle constant. I just took the carb apart and the pilot jet was mostly clogged and I cleaned it. The first start up it idled great all by itself with the choke on for about 1 minute then reved way up and ran like crap all over again.

Any suggestions for fuel screw or jet changes or anything else??? I am a newbie with the newer 4-strokes.


Are you familiar with the operation of the hot start valve (the red pull knob next to the black choke knob)?

yes, I am familiar but have yet to use it because I can not get the bike to run good enough to be hot.......and mine is on the handle bars.

1 hour ago I changed on my 2000 yz426. Needle from a 01 yz426 and went up one size on main jet 165,Wow huge difference this was the best 20.00 dollars i've put In bike.

No more Idle Issues / Popping

So, then, there is no red knob on the carb, and there is a cable coming from the left side of the carb, near the choke to the aforementioned lever?

That being the case, be certain that the cable and hot start plunger is free, and that it closes completely. Check the cable for play. One way to tell is to operate the lever while the choke is on. Under normal conditions, it will work like a thumb throttle, raising the idle speed significantly when opened, and dropping it back when released.

If that turns up nothing, look for other causes of running lean, such as air leaks, clogged jets, or a tight intake valve. Very low float level can do it as well.

Another thing is the spring plate on the engine side of the throttle slide. It should be positioned so that the square edge is down, which will put a small hole at 6:00 o'clock. They can become cracked and loose pieces of the edge, or be incorrectly installed, and cause the engine to run very poorly at less than full throttle.

I will still have to check the hot start lever during idle with the choke on but I did go up to a 170 main and a 48 pilot. This seems to have made a big difference. Not nearly as much popping but I barely got it warmed up and did not have time to play with the idle speed. I also have the fuel screw out 1 3/4 turns and the idle valve out about 4 turns to get the idle with choke low enough. Thanks for the help!!

i had simular situation when i got my 00 426. fought it for month. then i took it to the dunes and road the crap out of it all day and the more i rode the better it ran.now it iddles and does not pop at all.

FYI, if you decide you want to make that monster a little more quiet...DO NOT get the quiet core insert. I noticed LITTLE TO NO differnce.

just my .02

Hi My 01 yz426 is having the exact same fault but i can't put my finger on whats wrong what did you do to eventually solve your problem any other advice as i'm so p~~~ed off seem to be going round in circles.


I have also encountered these problems with my 2000 YZ426... To solve the problem I installed the JD Jetting Kit and Zip Ty air/fuel screw so it was easier to adjust. Then I went to the local riding area with extra sparks plugs and all the jets and needles. I spent 8 hours trying differant jets, needles, needle placement and air screw until there was no bogging or popping. Needless to say it was the best 8 hours I spent working on my bike. Just rember each bike is differant and it takes time to get the bike dialed in, but once it running right you'll enjoy the bike.... Just my $.02....

that what my wr400 is doing mate i am waiting for a anser. if you find out can you email me please,bri2265@hotmail.com


FYI, if you decide you want to make that monster a little more quiet...DO NOT get the quiet core insert. I noticed LITTLE TO NO differnce.

just my .02

Actually, it DOES make a difference.

Just NOT at the bike, but away from the bike is where you notice it - it's all about where the sound gets dispersed to, the problem with the supertrapp exhaust style is it dissipates the noise in all directions about 90 degrees to the bike except back because of the plate.

Get the quiet insert and lose the plate, now most of your noise gets directed back/down - yes you still hear it, but walk 20-40 feet from the bike and the difference will be astounding.

If the above bike was jetted for 3000 feet, that means at 3000 it's pulling in thinner air, so a leaner jet is needed because there's less air in the same amount of space compared to sea level.

So at sea level you would require a bigger jet to allow more fuel through.

your pilot jet plugged up again clean the carb real good than it should run like a champ

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