mid range issue with 02 426

Hi gang. A friend of mine recently bought a low miles easy ridden 02 WR 426. The main and idle circuits are dialed in. Good idle, great top end. The midrange is erratic. We dropped and raised the needle one notch and neither helped. I was wondering if there is an inherent quirk with these we dont know about. Ran some carb cleaner thru it and about 2 tanks of gas.

Any help will be appreciated. Frank :thumbsup:

Hmmm.... nothing comes to mind. Can you give us more details? Maniac

Well, since it idles and runs out to top end fine, Im thinking its isolated to the midrange or needle setting. We went both ways on the clip with no improvement. We may need to go 2 settings one way or the other to see a change. I just thought someone may know a trick for 8500 feet, such as a different needle.

JD jet kit will work wonders! I've run them in everyone of my Yamaha's. Have you posted this in the Jetting section too? You'll get more responses. Maniac

Are you running at about 30-35 in 3rd gear, at a constant speed? If so, it seems like most 426's do that. My 01 WR will surge and settle, surge and settle if I am just cruising down the road at a steady speed. I never notice while on the trail because I am never holding the RPM steady enough. The other common issue is that it could be the Throttle Position Sensor (TPS) needing calibration. I personally never recalibrated the TPS, but I think it does help clean this up.

From the FAQ 5th question down:

"Q: Why does my WR seem to miss when I hold the throttle steady in the 1/4 to 1/2 turn range?

A: That's your TPS (Throttle Position Sensor) doing it's job. Dirt bikes don't normally run with a steady throttle off road and they weren't designed too. Unplug it and see if the "miss" goes away. If so, then you know. You can also follow the procedure for checking the TPS voltage in the manual. It's extremely simple if you have a multimeter and some folks have found that it is set funky from the factory. Once properly adjusted, the problem goes away."

Edited by Pooley

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