pilot air screw adjustment-please explain!

7 replies to this topic
  • michaeltrundle

Posted August 11, 2002 - 01:26 AM


I have just purchased a 162 Main Air Jet (they didn't have a 160 in stock) and an adjustable pilot air screw. I intend to run a 160 Main Jet, 38 Pilot Jet and an OBELN needle pos 3 with these.(rest of mods in signature)
My question is, How do you adjust the pilot air screw to represent pilot air jet size?
How many turns from fully seated does it take to get a 60 paj size? for example, and what size Piot Air Jet is best matched to the 38 Pilot jet.
Any advice from anyone running the smaller'taffy' style of jets or the adjustable Pilot Air Screw will me much appreciated, taffy? jd? anyone! anyone!
I intend to go to yz timing as well soon, will my intended jets be in the ballpark for that change or doesn't the yz timing make much difference to jetting requirements?
thanks in advance for any help!

  • ejr

Posted August 11, 2002 - 04:43 AM


Check your e-mail or read this

[ August 11, 2002: Message edited by: ejr ]

  • tk421

Posted August 11, 2002 - 11:36 AM


From seated, slightly less than half a turn equals a 60paj.

A 38 pilot jet equals a 60 paj.

  • James_Dean

Posted August 11, 2002 - 05:32 PM


ejr's reference to the Patrick Burn's article has the "chart" with equivalent number of turns to match different pilot air jet sizes.

With a #38 pilot jet you should be down in the range of 3/8 to 1/2 turns out on the air screw from lightly seated to get a #55 to #65 pilot air jet. Taffy makes most of his posts assuming you have this chart to see how many turns he's recommending on the air screw.

A #38 pilot jet with #60 pilot air jet sounds like a good plan to try.

Good Luck!

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  • michaeltrundle

Posted August 11, 2002 - 06:08 PM


thanks a lot for the advice guys, especially the article with the chart in it from EJR.
I,ll put it all to good use in my search for more power and telepathic throttle response.
thanks again

  • ejr

Posted August 12, 2002 - 12:37 PM


J.D. have you seen that new version anywere?I have it on paper but not the acual file.Perhaps i should scan it as it is a much better than the one i posted.

  • James_Dean

Posted August 13, 2002 - 07:55 PM


It's gone from the previous location. Someone found it on Holeshot, but without the graphics.


[ August 13, 2002: Message edited by: James Dean ]

  • ejr

Posted August 14, 2002 - 12:53 PM


To go a step further than the article i posted.
Keep in mind i do not have a yz426 but it is an fcr carb which may or may not work. Anyway to set that slow air screw i take off the rear of the bike to allow access to the intake of the carb. I then start it, let it warm up and adjust the idle speed up to 1800rpm's or so.Then i turn that screw out until i get the highest idle speed.It's important to stop there because turning it out further will just lean the mixture with no noticeable effect on the idle.
I have had very good results with this method and have read on other message boards of others doing the same.


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