Jetting Specs

3 replies to this topic
  • cowboyona426

Posted May 01, 2001 - 06:12 PM


I was wondering if anyone could help me get my 2000 YZ426F jetted correctly. I am running a stock engine with an FMF Power Core IV (old round core design) spark arrestor. I am running a 167 main (+5 from stock) with the pilot screw 5/8 turn out, as recommended by FMF. My bike is running too rich though. I ride in Idaho at higher altitudes. If anyone has any suggestions I would appreciate it.

  • Boit

Posted May 02, 2001 - 06:40 PM


I'm at sea level and am running a #158 main jet..stock pilot at 1 3/4 out. I'm also using VP C-12 fuel and have the Factory R&D P38 acclerator pump plate. At higher altitudes, isn't it necessary to run leaner jetting to compensate for less air?
What are your symptoms? Does the engine blubber from the high mid-range up? Are you sure your jet is a #167? I wasn't aware that there was one of that size. This bike is very easy to change main jets. I can do it in less than 5 minutes.

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  • JBM

Posted May 03, 2001 - 05:10 AM


I'm at about 4000 ft. and I am running the stock 42 pilot, pilot screw at 1 3/4 to 2 turns out, stock 162 main, stock needle with the clip in 3rd position which in one up from stock, needle is dropped. So really the only change I've made is going one clip leaner on the needle. I run pump premium and am in New Mexico. This runs crisp for me.

  • Guest_Guest_*

Posted May 04, 2001 - 07:59 AM


I have a 2000 YZ with a FMF Powercore 4^2. I run stock header pipe, stock mixture, stock needle with a 152 main. I'm in Colorado from 5,000-13,500 ft with no jetting changes ever. The 152 was tested on the Dyno at Performance Cylce of Colorado. I think I run the leanest jetting from anyone on the list and have never had a plug foul or anything. Weird I guess.

Roostn in Denver

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