part throttle stumble

I just picked up an 04 WR450 w/ a PC 496 pipe, it had been sitting for about a year with the gas still in the carb. I dumped all the gas, removed the carb and cleaned everything out completely then reinstalled it. Filled the tank with fresh gas and it fired right up. A quick rap of the throttle works great, the problem is when riding down the road at about 1/8 throttle, it has a severe stumble then picks up as more gas is applied. Pulled the carb back off and cleaned it again, still the problem. It has a 170 main jet, 45 pilot jet, mixture screw @ 1 3/4 turns out as recommended by PC. Any suggestions?

I had a part throttle stumble on my bike a while back too, it was a jetting issue. If I remember right, I had to mess with the pilot jet/fuel screw/needle to sort it out. Check out the WR jetting database sticky on this forum to search for other WR's jetting specs. If you ride anywhere from 1000' to 5000' altitude the jetting shuld be pretty straight forward.

If the bike sat for that long with gas in the carb, I would replace the pilot jet with a new one....just to be safe. Make sure the your needle clip is in the middle groove, and set your fuel screw at 2 turns out. See if that helps.

I had the exact same problem initailly. With the pilot jet/main jet/needle dialed in and a fuel screw that I could get at easily (stealth) fixed it with some tinkering. I still get that same stutter when its cold- bike needs to be run for about 10 minutes and then its great.

If you're going to replace the pilot anyway, you may want to give a 48 a try... :busted:

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