WR426 Starting Issues - Help! :)

Hi all - I picked up a well-maintained '02 WR426F last summer, and it has been a great bike for me. At first it would start on the first 3 or 4 kicks, but last fall (and this spring again), the bike has been incredibly hard to start cold.

If the bike hasn't been started in 12 hours or so, it now can take me 20 minutes or longer to start this bike. Once I get it started and warmed up, it's fine. Once I'm riding, if I decide to shut it off, I usually re-start the bike first kick.

Also, something new that just started is some backfiring. It actually backfired when I was holding down decomp. lever and kicking to clear carb, and then also some when I was riding the other day.

I don't get out that often, sometimes weeks between rides, but I'm running fresh gas, and I checked and cleaned plug.

What should I check? Rip apart the carb and clean it? Do I just clean with aerosol carb cleaner, or should I soak the carb in Berrymans (or an equivalent)? I've never had the carb off this bike, so I'm a bit scared to do this (I have limited mechanical apptitude, but I'm willing to learn lol). What's this about TPS - I leave it on when I clean?

I know I have lots of questions, sorry for being a noob. I REALLY will appreciate any help any of you guys can give me!



If it is only hard to cold start when the outside temp is really cold it is most likely simply a too lean pilot jet. Being too lean will also cause the popping/backfiring on deceleration. Check your fuel screw...see how many turns out your fuel screw is by turning it in until it stops. Then try turning it out an additional 1/2 to 1 turn beyond where it was. If you turn it out three full turns and it doesn't help then you should rejet with the next larger size pilot jet.

I would also check your valve clearances, once they tighten up it will cause difficult starting even though it still runs fine once started.

One last thing...when it is very cold outside the fuel doesn't vaporize very well since the carburetor/intake is so cold and it may be necessary to twist the throttle a few times before kicking it over.

It's not just causing me difficulties when it's cold out. For the last 2 months of riding last fall, temperatures were still 15-20 Celcius (59 - 68F), and I was having these difficulties.

The bike was in my garage (kept at about 60 degrees Farenheit) all winter, and it wasn't below freezing outside when i tried to start it the other day (bike still in garage with garage door open a bit for exhaust fumes).

Although I'm not disputing that the bike is running lean, (the pipe glows cherry red right away when started in my garage, another indicator perhaps?), I'm certain the temperature is not a factor here at all.

The valve clearances might be the issue, I've never had them checked. I have no idea how to do this, how much should I expect my Yamaha shop to check this for me? By "checking" the clearances, do they also adjust them if there's an issue, or does "checking" mean merely diagnosing a major repair?

Then my first thought would be that your valves are out of adjustment. Checking/adjusting valve clearance is not hard and it is not considered 'repair'...it is simply maintenance. Get a manual for your bike and it takes you step by step through the process.

I’d break the valve maintenance into two steps. Checking and Adjusting. Checking: The hardest part about checking the valves is getting the valve cover off. I can only testify about my aluminum frame bike, but it took 3 hours for me to get that thing off. But I recommend checking yourself. Very little harm can be done. Unless you forget how to put it back together.

Adjusting: If you check and find that you need adjustment, then you’ll have to figure out if you want to take it to the shop or do it yourself. At this point you know the bike needs fixing so its easy to justify the money. But. that is going to be your own call. You have to remove the cams to shim them and you can seriously mess things up. So, if you know how to use a torq wrench, think you can degree a cam and know to plug holes with shop rags; then go for it.

Not to dispute anything here , but even in the garage the winter barometric pressure will affect the jetting. If you have the carb off then I would recommend checking the o-ring on the removeable needle seat and clean the screen while it's out. Another thing that can cause an issue is if the jet needle and the needle jet (2 different things) are worn. Just a few more things to think about. Checking the valves is never a bad thing, but I would do it myself as I have a lot of doubts that you will even get your bike into a shop around Calgary anyway. Most of the dealers won't work on any bikes older than 5 years and the rest of the independant shops are so busy because of that , they are booking 3 months out. Time to download a manual from the WR performance section and get out in the garage. . WR Dave.

WR Dave, this is Simon's (chucker from Calgary) old bike, I've only got about 50 hours on it since I bought it, and I'm sure that he had the valves in spec, but I guess I'll need to check them nevertheless. I'm also going to take the carb apart and also take a look at the things you mentioned.


The hardest part about checking the valves is getting the valve cover off. I can only testify about my aluminum frame bike, but it took 3 hours for me to get that thing off.

On the steel frame WRs, getting the valve cover off is much easier. I had the cover off, clearances checked (all in spec :prof:), and everything back together in about half an hour last time I did them.

Just to repeat what everyone lse has said.

check and adjust your valves.

The temp will have an effect on starting, give the throttle a couple of extra twists. You should check your fuel screw and may need to richen the pilot circuit.

Question - if my valves clearances are tight, why will this affect cold starting, but not be an issue when the bike is warmed up?

Another questions, hopefully not too stupid: This WR426 has YZ camshaft timing, does that change my specs for valve clearances, lol? Hopefully I can still follow the valve specs in my Yamaha manual...

If the valves are tight then they could be held open slightly affecting the ability of the cylinder to pull any fuel mixture from the carb. Being that is was Simon's bike I think it would have been pretty well cared for, but checking is free. YZ timing is the way to go on this engine and it doesn't change the clearance specs at all. Just make sure you check everything on the carb when you have it out and pay close attention to some of the items I mentioned earlier. The needle jet and jet needle can wear on each other and throw off the mixture to the engine. Ever try to start a flooded 4 stroke? My guess is it is fuel, as when the engine is warm the fuel evaporates quicker and doesn't cause as much of a problem with starting, not so when engine is cold. Give the AP squirt a good look when you first remove the carb as well, it needs to be approx 1/2 sec in duration, no more. ONE MORE THING (I'm not yelling, I just want this to get across) ALWAYS SET THE ENGINE TO TDC WITH THE KICKSTART LEVER WHEN THE ENGINE IS NOT RUNNING, that way the valves stay at the most relaxed position in the engine for extended off periods, therby preventing a stuck or hung open valve. :prof: WR Dave.

On the steel frame WRs, getting the valve cover off is much easier. I had the cover off, clearances checked (all in spec :prof:), and everything back together in about half an hour last time I did them.

work on my 08 is like working on a "ship in a bottle". :confused:

there is a trick to it. I'm sure next time it will only take me 30 min to get it off. but the first time was an adventure :bonk:

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