Mid-range sputter.

I have been experiencing a lot of mid-range sputter with my 2001 WR426. I live at 4,500' above sea level (Salt Lake City) and have the problem at areas as low as 3,500'(Moab, Utah). I took my bike in to the local dealer's shop and they said that if I can live with it, to just leave it alone. They said that if it really bothered me, then they would order in a jet kit and try to figure out the jetting. Of note, my spark plug has fouled once, and when I cleaned it at 300 miles it was tarry black.

My question, has anyone else in SLC, UT experince the same problem and if so what carb settings are you currently running. Any suggestions would also be appreciated.


Ha! Find a new dealer, get new jets & punch in "jetting " on the TT search.

I ride a '00 400F. I had the same problem with sputter but at a lower altitude(Boise, ID, 2800). My sputter varied with the several different exhaust system combinations I tried. I settled in on a stock pipe with the White Brothers VORTIP baffle then fiddled with the jetting to get perfection. Once the jetting was right my sputter disappeared. I ride from the lowest valley areas at 2800 feet to the top of the rockies at 10,000+ without problems.

Get your jetting set correctly and you will be in Heaven.


Originally posted by littlemeh:

mid-range sputter

I live at 4000' and had the same problem. You are rich on the needle circuit. Drop the needle one clip position and this will help out the problem. If the problem persists, you may even have to try two clip positions.


Follow yzernie's advice.

Cheapest mod(nothing to buy) to your problem up is rasing the clip position from #4(stock) to #3. You'll notice a big difference for such a small move.

Only adjust the main jet if your getting splutter also at full throttle(do the position mod first though). But I suspect your only getting trouble from 1/4 to 3/4 throtle right? Well it's all needle position.


You are right. All of my problems are at 1/4 to 3/4 throttle. I have also fouled two plugs in 300 miles and they are a sticky black. The bike now has around 400 miles on it and the problem seems to be worse with the cooler weather.

I'll try your and Yzernie's advice and change the needle position first before I have the shop mess around with the jetting.

Thanks for all of you help,


My 400 sputters at mid throttle too only when It's like 50 degrees. I thought that this problem was too little fuel at mid throttle. so raising the clip position whould make it leaner yet. I realize that your plug is fouling so maybe you have a rich idle path and a lean clip setup??


To confuse you even more, in winter months, your bike will run leaner:

1 - less moisture in the air means more O2

relative to moisture content

2 - cold air is more dense - more O2 per unit


Winter months means jet richer on a PROPERLY jetted carb.

Your ballpark stock jetting should be based at sea level elevations. The higher the altitude, the less O2, meaning you have to jet leaner...

Tar black plug...That IS impressive - mucho rich!


I had the exact same problems you are describing. The bike ran great until I had about 500 miles on it and it got colder out. I started to get a mid throttle sputter. It got so bad it fouled the plug. I know conventional wisdom says to jet richer in colder weather. For some reason my bike became very rich in the colder weather. I leaned the needle out one clip and it is now running great.

I know it was cold here yesterday at 40 degrees, hardly a cloud in the sky but the humidity was at 87% I think possibly though the winters are dry fall can be very wet and humid causing the bike to run rich. Maybe a bar mounted weather barometer would be an good add on :)

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