01 Jetting fmf

4 replies to this topic
  • canavero

Posted August 30, 2001 - 03:41 AM


First Thanks for all the info and goodwill extended in this forum. This is my first post as I have been able to find everything by searching; however, I do have a jetting question.

I live at 5000 and ride between 4000 and 6000. I have used stock pipe and jetting and have been happy. I just switched to a fmf pwr core 4 sq and it ran horrible. Please advise on jetting specs. Current - 01 426 with 45, 175, 4th position, 2 1/8 out.


  • Scooter426

Posted August 30, 2001 - 05:49 AM


175 main seems awful big for your altitude. Stock is 162, and you should be smaller than that by ~2 sizes. A good rule of thumb for jet sizes is one step for every 2000 feet in elevation.

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  • troyoda

Posted August 30, 2001 - 08:58 AM


Both the pilot and the main seem awfully rich. I’d suggest going back to the stock setting, which I think is a 42 PJ and I do think the MJ is a 162. I’ve got a 01 426 with a DSP pipe and I’m using a 45 PJ with 1 1/4 turns out on the screw and a 168 MJ. This works for me up to 2,000 feet. I’m not an expert here, but I think the higher flow rate of the FMF pipe might compensate for the higher elevation.

  • mikeolichney

Posted August 30, 2001 - 10:37 AM


I think you are running too rich, even though you have changed the pipe. I ride MX/HS at 5000 ASL and currently am running a 155 main, stock needle, clip #3, 40 pilot, FS 1.5 turns out on my stock 01 YZ426. My bike runs great. When the temp is in the 90s I run a 152 main and go 1 turn out on the FS. I have a Alt/temp jetting chart that works well for the YZ426, email me at mikeolichney@hotmail.com for one. (I am going to Crested Butte for a week so it may take a while to get it to you).

  • BikeDestroyer

Posted August 30, 2001 - 11:07 AM


If you call FMF they are very helpful on jetting changes with their pipes.

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