Mysterious Pilot Air Jet 2 on WR400 FCR39H carb?

2 replies to this topic
  • bultaco

Posted July 29, 2009 - 03:14 PM


I am replacing all of the jets and valve seat in my carb...Does this pilot air jet 2 exist? I am looking at the schematic in two different service one it is numbered 6 in the other shows that it is located somewhat below or next to the choke origin in the throttle body...Is it the small deep hole underneath it behind the flat bracket??????? Manual says that standard pilot air jet 1 is #75 and standard pilot air jet 2 is #90.

The only variations on my carb from stock are:

Stock Mine

Jet needle DTM-3 OBDTM

Pilot Jet #45 #48

Starter Jet 1 #65 #60

I have an aftermarket header and FMF e series pipe (12 disks)

Has be VERY tough to I am replacing all jets (with current sizes), needle, valve seat, gaskets, a c pump diaphragm, cleaning. Previous owner said bike ran well with before. I also changed the exhaust can to a auto decompression with correct .20 valve clearance as Hot Cams instructed...Intake clearances were in spec.

Any insight appreciated.

Thanks so much.

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  • bg10459

Posted July 29, 2009 - 05:03 PM


The pilot air jet controls the vacuum signal at the pilot jet. The bigger the PAJ, the greater the vacuum signal will be at the PJ. If you were to switch from the 75 to the 90, you would have to reduce the PJ size to prevent it becoming overly rich because the greater vacuum would pull more fuel through the PJ. There's more to it when you consider the ACV, but it's been too long and I'm no longer well versed on the issue.

  • bg10459

Posted July 30, 2009 - 04:43 AM


Starter Jet.....#60

Has be VERY tough to start....

I just re-read this part. If it's tough to start with the choke, this may be why. The starter jet is only for the choke circuit. #60 seems pretty lean. If not, try turning the idle up a bit. The pilot should be good between the 45 and 48.


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