pilot air jet

I have been reading through the forum now for a couple of months and have come across a couple of threads where people have said they have removed the pilot air jet.

Why has this been done and what does it do.

Is this on fcr or mikuni carbs.


It's only for some FcrMX carbs , not for Mikuni or older fcr models .

The removal of the pilot air jet leans the circuit out to the correct mixture , taking into account the other mods done to the carb .

It only applies to the Sudco 016-925 FCR-MX39 models due to overly rich pilot circuits with the #45 PJ.I removed the #100 PAJ from mine and it never idled right.IMHO it needs to remain and the idle circuit works better with a #42 PJ and a 9mm float level setting on an all stock motor.

PAJ removal is also is appropriate with the TT and Epic Fcrmx conversion kits (which is the same part no.)

With an EMN needle running without the PAJ is not an issue...45 pj is still normally used....

Hello everyone, not to jump into the conversation, but glad I found a recent posting regarding the Pilot air jet..I currently know I need a larger main jet (currently148) getting a 150,155,160 to try. I have a 45 pilot jet, and CE removed and capped, First start up with paj in and current set up only would idle perfectly with R&d fuel screw all the way in.

Removed vacuum caps, linked two with vacuum still left paj in and got a comfortble idle adjusted with fuel screw two out.

Took it out for test ride ran ok, no popping or rough spots..except the "off idle bog" I am guessing is what it was. Again I know I need a larger main but my question is what is the best set up? with the pilot air jet removal/100 instead of stock 60/ or vacuum two together? Thanks for any input..

Currently 0-1500ft

K&N, full yosh rs2, 3x3

148 main

45 pilot

R&d fuel screw 2 out

60 Pilot air jet in

I found the 45 pilot was too large, Here are my results.


For a 45 pilot jet, you should be running a 100 pilot air jet.


A 60 pilot air jet would be more approiate for a 38 Pilot jet.

No.  With the carb (I think you have, OEM Suzuki FCR, you have not identified it) the pilot air jet is always left in.  You have 2 options.  CE removed and the nipples capped use 100 PAJ. CE removed and the nipples connected use the original 60 PAJ.  Actually there is a 3rd option. The PAJ is replaced wih a adjustable pilot air screw.  Run a 160 main.  What needle? That is pretty critical.


Off idle bog is probably the Accelerator Pump (AP)  You need to determine if it is too much AP, too long AP or not enough AP.  Usually it is too long.  AP delivery of about 1 second duration seems to be the best.  My technique is to limit pump stroke with a slug under the diaphragm.  Others wire the linkage together but now you have to modify the diaphragm for more stroke.

Yes, sorry it is the oem drz400 fcr. Oe needle I believe. Not sure what the designation for it is.

Any info on how to check my AP? A slug?

How to check AP (delivery time). Take the carb off.  With gas in the bowl, operate the throttle drum and observe the AP squirt.  You can see if it squirts or not.  You can estimate the squirt time.


A slug?  Are you asking what is a slug?  It is a piece of material placed in a place where it (usually) does not belong.  To "slug" a weld is to place a piece of metal in a weld groove and weld around it to avoid filling the groove completely with weld metal.  In the case of the AP, a slug is a piece of metal placed below the diaphragm to limit the travel of the diaphragm.  The spring in the operating lever allows the plump to stop and the operating link to continue to travel.  I made some small brass spacers of various length to "tune" the AP time.  Much less than 1 sec and the AP did not work at all.

Ok. I will have to check it out and see how long it is. I appreciate your time. I suppose I will order a 100 paj to be able to cap off rather than see a vacuum line on. Any recommendations on needle type and clip position? I work for suzuki/kawasaki so I would like to simply find a oe needle that works best that I can special order. What main would you suggest?

Stock OBDXP clip 5 works OK.  Better for performance is EMN -3.   I think there may be a Yamaha P/N for the EMN.  Look up 5JG-14916-MN-00 (or try 000)


Main jet size? 160. (post #8)

What would your recommendation be on jetting differences with a NCYR needle vs. EMN needle? Main still a 160? What about clip position? Waiting on jets r us to send air jet to go back together. Thanks

What would your recommendation be on jetting differences with a NCYR needle vs. EMN needle? Main still a 160? What about clip position? Waiting on jets r us to send air jet to go back together. Thanks


If I may......you need to use a slightly larger main jet if you wish to use the NCYR needle, this needle has a leaner straight diameter and less taper than EMN..delivering a less aggressive throttle response...  with the leaner straight diameter you should be able to leave the pilot air jet in with fcrmx....

At small throttle openings air/fuel readings will be leaner than stock or emn needle........Also note the straight diameter of NCYR  is leaner than the oem E needle, .

For NCYR I would suggest using clip 2 

Are you sure about that needle code?  I only know 5 digit or 3 digit. 5 digit the first 2 letters are the material. OB is aluminum. OC (I think) is copper.  You do not care about the material.  The next 3 digits (or only 3 digits) is the taper, length and diameter of the needle. That is what you care about.  I don't know what a NCYR needle is.  Seems like I have seen it someplace before but my memory fails.

Excellent information. Thank you very much. I believe I will order me a EMN tomorrow from my yamaha connection. Then I will use a 160 main 100 paj and my 45 pilot and see from there...clip position on EMN?

Craigo - So probably no point in using a NCYR to replace a DXP if a person already has the DXP.  Who would want to go leaner than stock?

07 - Post #13. clip position 3.  Always count from the top.

Craigo - So probably no point in using a NCYR to replace a DXP if a person already has the DXP.  Who would want to go leaner than stock?



The NCYR is a needle code used as oem by some manufacturers.....

It's suitable for some applications but not a desirable needle in my mind...

Edited by Craigo 485sm

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