Got my first bike! `02 WR426... need some help

Hello all,

I bought this bike knowing that the cam chain needed to be replaced. I replaced the cam chain and 2 intake valves that got bent with the timing out. I also adjusted valve clearances and cleaned the carb. Spark plug is ok I think I'll replace it too just in case.

My problem is that it will start with the choke but shuts off when I push the choke back in. From what I read the pilot jet needs to be replaced. I'm planning on doing that tomorrow. One difference I have is, after it shuts off I cannot restart it is this problem related to the pilot jet or something else?

Thanks for you help!

You are probably on the right track. Take apart the carb and clean it thoroughly, blow out the passages with compressed air and reassemble. Remember to put the slide back in the proper orientation (a very common mistake). While you have everything apart, write down all the jet sizes, clip position of the needle and the needle code.

Depending on your riding experience, take your time with unleashing the beast, if it has not been already as the power can be very unforgiving. This bike has a long list of free modifications to do to increase power. The absolute best mod to do (in my opinion), regardless of anything else is the O-ring mod. Do a search on that to check it out. I would also check out the WR4xx Jetting Database thread and find folks in areas similar to your own, and see what kind of jetting they run.

Congrats on the bike. I still ride my WR426 and still absolutely love it.

Thanks for the reply. I did take the carb apart and clean it, I'm not too sure what the "slide" is tho? Also, it looks as tho most the mods have already been done, when I put a new cam chain on I did the YZ timing. But, I'm not too sure what the o-ring mod is I'll have to research that one.

Update: I started it again tonight and it looks like the idle speed was turned down too low. So, when I pushed the choke in the idle was too low and it quit. What I really need help with is starting it again after it has been started. I let it run for 5-10 mins tonight then couldn't get it to restart???

I tried using the hot start. It would stact like it's going to fire but would not run. The previous owner had the hot start installed on the handle bars hopefully it is working.

Also, I didn't take the carb apart down to that level so the plate should be installed correctly.

I also want to make sure my timing is correct. I have a question as to where the marks on the cam's need to be. On the intake cam for example: I've read that the "I" mark needs to line up with the edge at 3 o'clock, if I line it up exactly the top mark is not at 12 o'clock and the "E" mark on the intake cam at 9 o'clock dosen't line up with an edge. Is this correct? Or should the "I" and "E" marks on the cam have even spacing with the edge? Does this make sense?

I think I figured it out... I needed to figure out the knack to starting it.

So, now that I can ride it a little, at low throttle it feels kinda sluggish almost like a 2 stroke right before it kicks into the power band. It Any thoughts on this?

The 426 will bog quite a lot at low RPMs, especially if you really crack the throttle. The O-ring mod will help this tremendously and even out the low end 2 stroke like hit, as will appropriate jetting for your elevation and weather. The bike is a beast and the power definitely comes on abruptly, especially when it has the low end bog and following power surge. I think it was once described as one of the hardest hitting, most 2 stroke like powerband of the then-current four strokes.

For starting it, just remember...Top Dead Center (TDC), pull decomp and move the kickstarter 1 inch. Release decomp and kick the bike like you mean it. When it has been sitting for a while (longer than over night), twist the throttle one MAYBE 2 times to prime the engine and that is it. Then put your hand on the bike somewhere, AWAY from the throttle and kick the bike over. DO NOT give throttle while trying to kick, or you risk a kickback and a possible broken bone. It's happened to someone here. If you think you have flooded the carb, hold in the decomp lever and kick it 10 times or so just to clear things out. Then just try to start it as normal, without priming it with the throttle.

Once you've gotten the beast to fire up for the first time of the day, you should not need to prime it again. If you dump the bike and it has a ton of gas in the engine, you can try the hotstart, but may need to do the carb clearing procedure.

Mods to look into:


Grey Wire (ignition timing, especially important with YZ timing)

TPS adjustment

Chain slider (they don't fit tightly and can wear the top of the swing arm. most people put cut foam, or innertube underneath to make it fit better)

GYT-R exhaust tip, slip-on can, or full exhaust for better performance

Airbox lid removal

Throttle stop mod, or YZ stop replacement

ACV disable

Light blue wire (neutral detect)

If I remember more I'll post them.

Thanks Pooley you've been a huge help!

Here's what I know has been done:

FMF exhaust

Desert tank

Grey Wire

Chain slider

Airbox lid removal

YZ timing

Is there anywhere that show's how to do these other mods and what effect they have? I thought I saw something a month ago but I can't seem to find it again.

There were posts, but I think the recent forum changes (within the last month) have caused a lot of the posts to go away. Hopefully the forum gurus will be bringing back the old stuff.

Here is a link to the O-ring and jetting work I did.

Ok not so happy anymore :) I decided to go for a ride this afternoon, it started right up I rode it about 3 miles down the trail had to hit the brakes and it quit on me and would not restart. I tried to start it for 2 hours. I got it to start twice tested it out by riding for a minute, turning it off and trying to restart and I couldn't get it to start. I finally had to bring in the truck and load it up and go home.

Anyone have any ideas? I did notice that while kicking it, there was fuel coming out of the hose that comes from the very bottom of the carb (number 53 on the following diagram)

I would guess that the needle valve o-ring is old, hardened and is leaking, which would be #25 on the diagram overflowing the carb. The fuel dumping out of the tube could also be a float height being off or even the valve seat being worn. Turn your gas off, lay the bike over a bit to drain extra gas, then try and start the bike to see if you can get the bike to run for even a minute. This would indicate that the fuel level is just too high and is flooding the engine.

Last summer I had the needle valve o-ring go bad on me after 8 years and to definitively test it, I found some grease that I temporarily used on the o-ring to allow it to seal. The bike DID start and run for a few minutes, until the gas dissolved the grease. It's a really simple fix, although I think you have to buy the whole damn $50 assembly for a single o-ring.

I recently replaced my 0-ring. It was leaking out the carb overflow hose when the bike was not running and the petcock was not turned to off. I took the o-ring to the local checker auto parts store and matched one that they had in their selection drawer of carb o-rings. It solved the problem. you need to find the o-ring that is ok to use with gas.

Thanks Guys,

Sounds like I'm gonna be taking the carb apart again.

jcbikes, do you have the part number for that o-ring from checker?

Sorry I do not. I just picked one that matched out of the box of many. just take the old one with you and the needle valve that it goes on to.


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