yz250 with pro circuit

[dan151]

ive got a 99 yz250 with a pro circuit works pipe and fmf silencer. it has a 178 main, the needle is on the 2nd clip position, and the air screw is turned 1 1/2 turns. it ran great in the colder weather and now that its 90 degrees it fouls plugs like theres no tommorow i changed from 32:1 to 40:1. and it didnt change much at all. pro circuit reccomends on there site that you shhould use a 168 main? would that help if i changed to a 168 or would it be too lean?

[FPMXer]

It's what they have tested and tuned bikes with for that pipe and set up. You might also want to try and give the air screw another 1/2 to 3/4 turn out. But if your fouling plugs then yes bump down the main and even the pilot. Start small bumps if your not comfortable with the -10 jump.

[dan151]

yeah going down 10 in the main is a very lean jump so im gunna try 172 which is the stock jet and see how it runs, then probably go to 168 that they reccomended and see how it does.

[FPMXer]

It's also best to install a new plug with a jetting change to get the proper reading. plugs are cheaper than topends.

[dan151]

true! thanks for the help

[minitrucker83]

Ill be diggin into my 99yz250 for the same problem next weekend. I noticed your reply in my thread. Keep the thread updated if you dont mind when you figure it out.

Thanks Dustin

[dan151]

yeah i saw your thread when i came on the other day. im ordering a bunch of jets tommorow to try and lean it out and a bunch of new plugs. any idea what the difference between an iridium racing plug and a regular plug? does one run hotter then the other? cuz i heard that might throw the jetting off a little not sure though

[minitrucker83]

Originally Posted by dan151

yeah i saw your thread when i came on the other day. im ordering a bunch of jets tommorow to try and lean it out and a bunch of new plugs. any idea what the difference between an iridium racing plug and a regular plug? does one run hotter then the other? cuz i heard that might throw the jetting off a little not sure though

I could be wrong but the biggest benefit of running an iridium or platinum type plug is how long they last. With performance type vehicles I usually stick with standard type plugs. They're usually not in there long anyways.