jetting for aftermarket exaust

I have a 2008 crf250r and just installed full pro circuit exhaust. Bike seems to be cutting out when getting in the gas hard. Could this be from running lean now? Anyone have this setup and know what jet sizes you're running? I'm at 500 ft. above sea level 40-60 degrees F. 

I suggest you contact FMF for jetting recommendations.  As the manufacturer they should be able to help.  Surely they dynoed the thing during R&D and have this data.

Tim, notice that the FMF jetting recommendations are for a nominal of 70°F,

in 40°-60°F ambiant temps you will no doubt have to go a tad richer.

Edited by mlatour

Multipliers for temperature:

  • 40F = 1.03
  • 60F = 1.01

Multiplier for 500 feet:

  • 0.996


  • 0.996 x 1.01 = 1.006 (189 main)
  • 0.996 x 1.03 = 1.026 (192 main)

Should be very close...

Edited by VortecCPI

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