tuning problems

I have a 01 WR426 with the bk carb mod, yz cam timing, blue wire and grey wire mod as well as a full system DSP eshaust. It ran fine for the longest time with all the stock carb settings and then all of the sudden it began to back fire really bad and not rev out cleanly. I took off the carb and cleaned it and put it back together and now I cant get it to rev out well. I will set the fuel screw and idle adjust so that while the bike is not moving it appears to run ok. But when I get on and ride it it begans to idle really high and won't drop back down again. If I lower the idle any it just quits. If anyong has any suggestions I would really appreciate it.

Backfiring and too high idle that finally returns to normal idle speed.

This sounds like a lean mixture.

What is the color of the spark plug?

When riding the bike and accel hard does it make a "boooaahhh" sound?

Check the hot start valve (not closing) and dissassemble the carb and clean all jets and passages.

I'm right there with you. The pipe was glowing red on idle, and was bogging really bad at about half throttle.

This weekend I dropped the clip position by two and it runs better now except for at idle. It'll die unless I've got the choke pulled out. I've got the fuel screw turned out about 4 turns. I'm thinking either the pilot jet / circuit is plugged or I've got an air leak around the boot.

I read in here to spray some WD-40 at the boots to see if they're leaking air. (It'll change the idle when it sucks in the 4D-40.) If all of that doesn't fix it, I'm going to stick in richer pilot jet.

Seems like the more I mess with it the worse it gets. :) It rips when it's running right though, worth the effort. :D

It'll die unless I've got the choke pulled out. I've got the fuel screw turned out about 4 turns.

Sounds like a lean condition to me!

Smoke :)

WHats the stock pilot jet? Hows your bike running smoke. My fuel screw is turned way out. Probably close to 4 turns. And it doesnt start that easy when its cold. I think I need to do some adjustments but Im not sure where?


Check all of those tiny holes in the PJ for blockage. Sounds like your suddenly lean.

Hindsight being 20-20, don't turn your fuel screw 4 turns out or it'll fall out of the hole. Or at least put some tape over the hole so when you're bike starts dying at idle you'll still have your screw to put back in the hole.


- Ryan

was the bike sitting for any length of time? Check and make sure the pilot jet is clear. Even a partially clogged pilot will cause headaches.............

Wildman- it sounds like you could have an air leak. Check your hot start, and the intake boot between the carb and head. Warm the bike up good(if possible), then spray wd-40 or contact cleaner around the boot at the carb and head while running. If you are sucking air, the engine rpm will change like Uncle G. said. Just a guess, but running stock jetting with all your mods may have been lean(especially if your not at high altitude). It may have been getting hot enough to warp or crack the intake boot at the head. :)

Good luck.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now