jetting tips

i am curious about jetting tips, i ride in and around bend oregon, at altitudes varying from 3000 to 6000 feet. i'm running stock jetting with my fuel screw turned out a quarter turn, this seemed to help the bog of the bottom but it still hesitates. i also have an fmf powercore 2 IV silencer and the power bomb header

thanks, discopete

[This message has been edited by discopete (edited 08-28-2000).]

[This message has been edited by discopete (edited 08-28-2000).]

[This message has been edited by discopete (edited 08-31-2000).]

What's the jetting that you are using now? Are you running the stock pipe? Are your valves adjusted properly? These can all have a direct effect on your low end performance. I hear it rains there quite a bit and the bike will also run rich in the rain (more moisture in the mix means less air).

You may want to start with the stock jetting (175 main, needle clip in the mid position) setup (if you aren't already) and make small adjustments until it feels right. A 3000 foot change in elevation while you are riding is pretty significant so it will definately fun rich at somepoint during your ride. I ride in varying terrain in Colorado and have found that a 168 main with the needle clip one leaner works for 7500 ft - 10,000 ft. If it was me and I was riding at 3000 ft - 6000 ft, (and I have a White Brothers E-series pipe with all the disks in it), I would keep the needle clip in the stock position and run a 170 main and see what happens. The popping sound you hear - mine has done that since the day I bought it (only when I let off at high RPM) and I have raced it all over Arizona and Colorado with no problems. I was told it was residual fuel burning but who knows. The type of gas you run as well as the octane rating can have something to do with it as well. Whatever you do, don't mess with the pilot. Good luck :>

[This message has been edited by coloradothumpin (edited 08-28-2000).]


What year/model bike do you have? The stock jetting is different from 98/99 to 2000 and from YZ to WRs. The spec.s Colorado gives above are for a 98/99 YZ. 426 stock jetting is 162/42.

If your bike pops on deceleration this may indicate a lean condition at idle. Lots of 426 owners have benefitted from a richer idle settings and richer pilots to alleviate low rpm "bog." Start with the idle mix setting before you try changing the pilot jet.

If you post more complete info. I'm sure you will attract the attention of some of the jetting gurus around here or someone with the same bike who rides in the same climate/altitude.

I'm in Colorado and have a FMF Powercore IV^2 Spark Arrestor mounted to a stock header pipe. I run a 150 main with the needle in stock position. I REALLY barks now with no popping on deceleration. My pooping with the stock pipe was due to being to rich with a 162 main jet.

I only ride trails and don't MX so this setup really seems to work well.

Roostn in Denver

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