02 wr426 stalling at idle

Hey guys,

Hoping that someone can help with a problem I have with my 02 426.

The bike runs like an absolute weapon and has absolutely no issues when it's going along. Problem is, when I pull up the bike will return to idle momuntarily and then just cut out. It starts up fine but the problem will continue if I move off again and then stop, same thing, the bike cuts out. If I leave the bike to idle it will idle fine, it only cuts out when I come to a stop.:busted:

Funny thing is that it does not happen if the bike is hot, say above 50 degress C.

Currently running e series pipe, disconnected tps, yz timing, emn needle on 3rd clip with 42 pilot and 175 main,,all else is stock.

I have changed the plug, checked that the fuel tank is venting properly, triple checked the carby is lined up with the air box boot, raised the needle all with no difference.

I was suspecting the needle was lean but the bike shows no other signs to support this.

Cheers, any ideas are greatly appreciated.


Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.


Thanks for the reply mate.

The 42 pilot is fine and I find that it is adjustable with the air screw (have an adjustable by hand one that you can count by the small wheel at the bottom) and it is suited for exactly two turns out. (wants to stall as it turns in and then not happy again 4 turns out). I also uped the idle a bit to 2200rpm thinking that it might help but still no good. The bike idles fine usually at 1750 (is what the trail tech vapour says), so I am at a loss to what the go is.


I suspect that it is just something that I will have to put up with and it's managable and a small trade of as the EMN needle absolutely screams.


Just means I will just have to stay on the throttle,,,will just have to live with it I guess :busted:


I have a question I am struggling with the same issue. The bike runs fine while I'm moving, but the moment I clutch it and coast the bike stalls. Or if I start it, it will only idle momentarily and then stall.

I have cleaned the whole carb. While cleaning it I noticed that the diaphragm located on left side of the carb (next to the hot start plunger) was cracking and needed to be replaced. Well I didn't have it so I installed it all back together.

Now my question is could that diaphragm cause the bike to stall like i explained?


1750 is a bit low

Your carb is old, so you need to replace the wear parts like the needle jet, slide plate and slide seal, if you want it to idle.


If you have an aluminum alloy fuel screw, get rid of it, as they are nearly impossible to get set right, as they have a taper.

You want brass, like the R&D.

My issue with my carb was that I installed the slide plate seal upside down, which seems to be the reason why it would stall after 5 sec of idling.

Once I flipped it, it idled perfectly.

Here is the link to the website that shows you the proper slide plate seal orientation


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