"Air" pilot jet - does anybody really know what it does?



9 replies to this topic
  • John_in_Long_Beach

Posted August 03, 2000 - 11:30 AM

#1

I know that a larger air pilot jet leans out the mixture for the idle circuit, that is obvious.

But what is the point of adjusting it if all adjustments can be made with the pilot jet.

The stock manual is quite good in the tuning section but nothing is mentioned about the "Air" pilot jet and when to adjust this instead of the pilot jet

I ask this question because I am going to go with the following set up.

DVP needle start at #4 position
180 main
48 pilot
DSP pipe and tapered header
YZ timing
airbox cover off

and it was recommended by one web site (stroker?) to go from a #75 (stock) to a #100 "Air" pilot jet. Why would I just not go down to a 45 pilot from a 48 pilot jet instead?

Thanks,

John Dumke

  • Kevin_in_New_Hampshire

Posted August 03, 2000 - 12:09 PM

#2

I went to the 100 air jet because I removed my octopus. From what I have read, Yamaha recommends to not mess w/ the air jet. But then again, I have seen "Bring it to your official Yamaha dealer".
Clark and James would be the guru's to answer your question.

------------------
99 WR, all YZ mods, de-octopused, OEM YZ tank and IMS seat, jetting by Clark/James, got forked by Pro Action, DSP airbox, PB Header, Stroker SX-1, Thumper Rad Guards, Acerbis Hand Guards, WAITING IMPATIENTLY FOR MOAB, boning up on my sheep shearing skills!!

  • SLO_JT

Posted August 03, 2000 - 12:12 PM

#3

See Clark's write-up about de-octopusing in the Technical section of the WR400 forum.

  • Hick

Posted August 03, 2000 - 01:22 PM

#4

Originally posted by John in Long Beach:
The stock manual is quite good in the tuning section but nothing is mentioned about the "Air" pilot jet and when to adjust this instead of the pilot jet
John Dumke


Actually, if I remember correctly, the tuning section in the back portion of the manual for my 426 states that if pilot jet is changed then pilot AIR jet must be changed. But then it says later that changing air jet is not recommended.

Of course, this is the same book that says that idle/fuel screw is set at factory and does not need to be adjusted :)

[This message has been edited by Hick (edited 08-03-2000).]

  • James_Dean

Posted August 03, 2000 - 03:03 PM

#5

I have tried the #45 and #48 pilot jets with both the #75 and #100 air jets in my '00WR. The #45 seemed best suited to the #75 while the #48 worked better with the #100.
--------------------
Keep in mind this is with the FCR2 ('00WR) and the differences were very slight. This is going to be different from bike to bike and altitude/temp. This was mostly at sea level and about 70 deg F.(#45 - 2-2 1/2 turns on pilot screw, #48 - 1-3/4 turns)
--------------------
- The #100 air jet makes it feel like the jetting is leaning out too much with the #45 just as I crack the throttle. Doesn't idle quite as steady.
- The #100 with the #48 pulls smoothly and feels like it would be less likely to stall, slip the clutch at near idle and it almost breaks the tire loose. (Like it best)
- The #75 with the #45 idled very good pulled smooth, but didn't feel as good torque wise as the 100/48. Was very good though, would consider it for higher altitudes. (Had fits of hard starting before the bike was broken in when I got it hot, maybe was just me)
- The #75 with the #48 worked good, a little more rich at idle, didn't think it pulled off-idle like it did with the #100.
---------------
Sudco rep told me the pilot air would affect mixture as the throttle was cracked open a little and it seems true.
James

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  • John_in_Long_Beach

Posted August 03, 2000 - 03:51 PM

#6

James,

Thanks for the explanation. More gas requires more air. Makes since

My bike is a 2000WR with following mods YZ timing, DSP pipe and tapered, 180 main, 48 pilot, air box lid off.

I am only changing the needle jet.

From a DRS needle in stock position (#3)
to
A DVP and I will try a position #4.

The question is

Since the DVP makes the idle a little more rich will the 45 or 48 be a better setup.

My experience previously is that the 45 was WAY to lean with the DRS needle.

But maybe the needle change will change this?

What do you think.

Thanks again,

John Dumke

  • Clark_Mason

Posted August 03, 2000 - 04:06 PM

#7

Try the 48PJ first and fine tune with the fuel screw. Start with the fuel screw at 1.5 turns out an go from there. This should be in the ball park. You are running with an excellet exhaust system and the jetting you will be trying will be vary close especially if you are running below 3000 feet of altitude.

Clark

  • James_Dean

Posted August 03, 2000 - 06:49 PM

#8

We agree.. :D :D :D :D :) :D

[This message has been edited by James Dean (edited 08-03-2000).]

  • Gordon

Posted August 04, 2000 - 03:53 AM

#9

James I've been running a 45 pliot, 180 main, and a OBEDVR needle in the 4th position runs and starts excellant. Can you tell me a little about this needle? I am yz timed, fmf powercore iv2 still waiting for my backordered power bomb. I have the carb apart with the 5jg14916-ep ready to go in but am getting nervous after reading some of the posts. So can you also tell me the difference in the two needles. I am running sea level to 7000 ft with existing setup.

  • James_Dean

Posted August 04, 2000 - 09:05 PM

#10

gordon,
-The last letter R and P reference the straight diameter of the needle. P is smaller by .02mm and will run a little richer at 1/8 throttle where the R is usually on the lean side. P is also .02mm leaner than a stock 98/99 WR M (DTM), so it falls in the middle.
-The tapers start at nearly the same location on the needle relative to the clip with the DV- and EK-. EM- is one clip leaner so it's taper starts .9mm lower. Since the E is more taper and P is a little richer also, the EKP will immediately transition to more fuel, I have recommended a leaner clip position by 1 slot. (DVR#4 to EKP#3 or EMP#4) Feedback has shown that maybe 2 clips will be needed for some setups. (DVR#4 to EKP#2 or EMP#3)
-Each bike setup is a little different so don't expect perfection without a little adjustment. It should be very close. I have tried to make recommendations in the middle of everyone's jetting by keeping track of the settings shown on the forum. Also by alot of testing on my own.
James




 
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