My awsome 426 starting to smoke

I acquired my 2001 WR 426 three years ago from a gentlemen that rode it twice and did not like it. I then immediately started adjusting it to fit all 6’6” 275 lbs of me. Flex bars, free mods, Quick shot, Z clutch, Race Tech fork and shock springs jets and I had a bike for once that fit me. (both of us big and heavy)

I am a woods rider and I have become quite fast as this bike and I work well together. The last couple of rides I have started to notice some white smoke more so when cold or under heavy accel. Maybe a slight loss of power.

I am meticulous with my maintenance. This bike has always started in one kick never hesitates, bogs or surges. I don’t even remember what jetting I ended up with as it has been flawless.

I am looking at the 444 big bore kit and I am somewhat hesitant as I do not want to end up with all kinds of drivability problems. I am spoiled with my now tired machine.

I think I would like to upgrade the power, what do you guys think? I hate to take it apart and not give her a little something. I guess I need to know the power difference and how I would need to jet it as I am so spoiled with how it runs know. Any thoughts would be most welcomed. Thanks.

Don't think twice about doing the 444 get more of a good thing.If you don't do cams, you get a power baqnd that pretty much parallels the stock one, just more across the board. It's a little slower to rev as you are moving more mass (heavier piston), and the revs also wind down a little slower, so you get a bit more of a compression braking effect. If you do a lot of woods type riding, I would stear clear of the high comp piston offered with the 444 kits. I have to run race gas in mine...


I have done all of what you are concerned about. I have an 01 426 with some motor work. I too was afraid that I would lose bottom end and it would become peaky like a two smoke. I was pleasantly surprised to find out that with a larger piston the motor is even better than before. When I bored the cylinder I also put in a set of hot cams and had the head ported. All of these mods really made the motor scream without sacrificing any bottom end power. I still ride single track, Baja and desert race and can't be happier with the mods I did to the motor, it works great everywhere. I wouldn't go with the high comp piston because then starting is harder and running Mexican gas is nearly out of the question.

As for jetting.... This was the most confusing part of the entire modification. I ended up going to smaller jets both on the main and pilot. I use a 168 main and 42 pilot. With the head work, cams and larger bore the motor actually acted as a larger pump therefore pulling more fuel through the same jets. I would presume that with just a larger bore and stock cams and head your jetting would be nearly the same. Nothing trial and error couldn't figure out.

If you have specific question PM me, I'm more than happy to share what I have done to my bike.


I, too, have the hot cams, ported, big bore mods done. My jetting is similar...170 main, 42 pilot, JD red needle on the third clip. I also have a quick shot and power now. I couldn't agree more that the power is great for the so cal desert. I do have to run race gas to keep in from pinging. The power even works great for kinda tight, rocky, twisty stuff like at KM. For slower, tighter woods type riding, though, the mid-range hit may be a bit much, and I would definitely stay at 12.5 to 1 to help with detonation as the motor gets good and hot.

What a great thread! :devil:

Thanks for the input it is appreciated very much. :devil:

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