New to me '01 426, ran good, now doesn't

Test rode on street, ran it through the gears and it ran very well and crisp. Took it out to the trails and it ran very well. Went riding yesterday and the bike did not run great. As long as I rolled the throttle on easy it was fine, but when giving it a healthy amount of throttle it would sputter.

fresh gas, plug looked fine. the only thing i changed from the previous 2 rides was a new air filter.

Any thoughts? Thanks.

Check out your Accelerator pump diaphragm see if any good if you open you thorttle open fast it should spray fuel in to the intake of the motor to much can make it bog to little make run lean.

Look up BK Carb mod

Check the jets and the bowl make sure you dont have dirt in it it could be a clogged jet.

On you new Air filter did you over oil the air filter.

Is your hot start valve all the ways closed if it hangsa open it run LEAN thats bad.

Is you chock off it cause to run rich.

Test rode on street, ran it through the gears and it ran very well and crisp. Took it out to the trails and it ran very well. Went riding yesterday and the bike did not run great. As long as I rolled the throttle on easy it was fine, but when giving it a healthy amount of throttle it would sputter.

fresh gas, plug looked fine. the only thing i changed from the previous 2 rides was a new air filter.

Any thoughts? Thanks.

Edited by marv02

Two things: You replaced the air filter; be sure it's not over-oiled, effectively clogging it. Secondly, the plug can "look fine" but be glazed with a semi-conductive deposit that can short under a load. Try a fresh one.

Also consider jetting issues if you test rode the bike on the street at lower elevation and in warmer weather.

Check your jetting to make sure that all jets are clean, proper for your elevation, temperature(s), and any mods done to the bike. Follow the stickies in the forums to tune each circuit. Do not assume that the previous owner did the job properly. It also sounds like you should check on the accelerator pump diaphragm and do the O-ring mod. In my experience, the O-ring mod was much, much better than the BK mod and a hell of a lot easier.

Edited by Pooley

Thanks for the replies fellas. Put in a new plug and that cured the mid range issue. Then found out the fuel screw was set fat for our altitude, turned it to 1 turn out and that fixed the 1/8-1/4 throttle hiccup. That was probably what caused the fouled plug as well.

More info on the o-ring mod please.

Thanks again.

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