Main Air jets

7 replies to this topic
  • racemile

Posted April 14, 2003 - 09:26 AM



I tore apart the Carb snd replace the MAJ's the PAJ was replaced with a PAJ screw set at 75. The MAJ that came out was a 200. So I replaced it with a new 200 and left my 162 main in.

Really didn't notice a major difference in how the bike preformed but I was out at Erie anyway (lower altitude)

Should I have noticed a large difference and are those the standard Air jets for the WR? I thought the standard MAJ was a 165?

Am I going the wrong way on this?


  • LarryCO

Posted April 14, 2003 - 09:31 AM


You lost me... :)

  • Hick

Posted April 14, 2003 - 10:25 AM


Standard MAJ is 200.

Standard PAJ is 75 (YZ is 100).

I think the 200 works well with a 160 main, smaller than that and you might try a 180 or 190 (if that is available). Since 200 is the largest size available the hot trend a few years back for guys at sea level running 165 + on the main was to run w/out the MAJ. A few guys even drilled out the passage to a larger size.

The air jets tend to affect mixture most noticeably at higher rpms, so a few high speed trips will jet the MAJ, use a simulated "freeway cruise" (low throttle but relatively high rpms) to jet the PAJ. Surging during cruising and popping of decel both mean the PAJ is too large.

What I do is jet for the pilot and main first. I even set the fuel screw for the best response, then I adjust the PAJ. Keep going smaller until it surges and pops on decel, then back off until this is gone. Then make a few high speed passes with a smaller MAJ, although if the 162 main is what is right for your bike I don't think anything smaller than a 200 MAJ will be an improvement.

Hope this helps.

  • racemile

Posted April 14, 2003 - 10:29 AM


hmmmmm.....I lost me...lets try this,

Replaced paj 75 with PAS set at 75.
Replaced MAJ 200 with new MAJ 200.
Replaced 40PJ with 38PJ

1. What are the stock MAJ in a 2002 WR 426? I thought they were 165's.

2. By going down on the pilot I got a bit better off throttle performance, but never had a hesitation with the 40PJ. Would these be expected results?

3. When I adjusted the fuel screw (new zip-ty) I raised the idle significantly and adjusted it between the changes in idle, then turned the idle down to acceptable levels. Is this the correct procedure?

There thats better,


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  • Hick

Posted April 14, 2003 - 10:31 AM


1) Stock MAJ is 200.

2) Yep.

3) Sounds okay to me. You may want to fine tune it based on throttle response off idle. If you then have popping on decel go smaller on the PAJ. FWIW I have a 40 pilot and my PAJ is about 85.

Hope this helps.

  • racemile

Posted April 14, 2003 - 02:37 PM


Thanks Hick, Larry!! So the 64 dollar question is:

What ratios should the mix be at? Barring weather, temp, etc...Shouldn't we be able to figure the jets sizes based on ratios and basic air pressure at altitude? Wouldn't this take a lot of the guess work out of tuning this beast?

Does anyone know these ratios?


  • Hick

Posted April 14, 2003 - 07:40 PM


Does anyone know these ratios?

Yes, but I never really bothered to make a note of them, because:

- you must have a good baseline
- climate/weather matters also
- different bikes and/or setups will respond differently to changes
- different fuels or inconsistent fuels also affect jetting
- rider preference and other conditions unrelated to climate are a factor

There is even a spreadsheet floating around here somewhere, I forget the origin but I believe at one point Motoman had this altitude/jetting spreadsheet posted on his website. But the results depend on the baseline, and we'll never get anybody to agree on that. :)

Assuming that the stock jetting may be a tiny bit lean, so that optimal settings at sea level will, in some instances, be richer than stock, and adding in a bit of my own experience at higher elevations, I would say that, at one mile of elevation, a good starting point is (drum roll please):

One to two sizes/steps leaner everywhere

Hope this helps. :D

  • Taffy

Posted April 15, 2003 - 06:36 AM


if you start with 35PJ-the smallest and the 45PAJ. you should then go up 15 on the air for every fuel jet so;
35PJ = 45 PAJ
42/90 PAJ
45/ about the same or 110

this is providing that you're running the correct needle. the needle straight should be **M or **N at sea level and **P or **Q at 5,000ft +

as for MAJ. DO NOT REMOVE THE MAJ. DO NOT DRILL IT OUT. after back to back tests it was found that with a euro pipe and YZ timing and "all the usual mods" the best MAJ was a #160. this gave the engine more over rev. the area of over rev is where you would normally jet the bike. infact the area that then needs the richest main jet is lower in the revs by 1-2,00 rves, so the MJ can then also be dropped by between 5-8.

good luck.



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