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  • Tap size?

    Replacing the adjusting needle in the GAV housing and the new one won't grab the internal threads. Brass threads must have been damaged then I took out old needle.

  • #2
    Have you put a drop of oil on the needle and pushed it in hard enough to overcome the wire ring tension on the end of the housing?


    • #3
      I took wire ring off and it still wont grab but a little and then skips off.....


      • #4
        I think its 1/4 24 NPT but not sure...


        • #5
          Here you go::: be very careful as mentioned in the illustration,,,


          4~ Tudor's
          1~ Coupe

          Henry Ford said,
          "It's all nuts and bolts"

          Mitch's Auto Service ctr


          • #6
            Thanks man but I had taken the parts to work and got a maint. guy to thread it. I just started my engine and she purrrrrs. I would like to thank the makers of RTV for sealing the cam leak. I've waited 20mins and no drips yet....I hope it's still that way when I wake up for night shift!!!! Winning!!


            • #7
              What I have found is the jets are 5mmX.75 pitch rather than the 10-34 shown above. The GAV needle is 1/4 X 24. Apparently that size is used on some Harley Davidson Cycles someplace. Not easy to find but I imagine all you to do us just need to push a little harder to get the needle into the housing past the little round spring at the bottom of the housing.


              • #8
                i just checked 3 carbs i have... the GAV is 1/8 pipe, and the jets are 10/32....
                the 10/34 in the pic above must be an error
                4~ Tudor's
                1~ Coupe

                Henry Ford said,
                "It's all nuts and bolts"

                Mitch's Auto Service ctr


                • #9
                  Yes, the gav housing is 1/8 pipe. I was referring to the needle that goes inside.


                  • #10
                    i was a little off target thinking he was talking about the housing,,,
                    4~ Tudor's
                    1~ Coupe

                    Henry Ford said,
                    "It's all nuts and bolts"

                    Mitch's Auto Service ctr


                    • #11
                      And here I thought all the internal threads were metric.
                      You wana look waaay far up da road and plan yer route because the brakes are far more of a suggestion than a command!


                      • #12
                        Sorry. It was the needle that goes inside and screws in GAV housing. Only needed to clean up 2 top threads and with some pressure it went in.


                        • #13
                          thats great to hear,,
                          Tom and Grover gave you great advice
                          4~ Tudor's
                          1~ Coupe

                          Henry Ford said,
                          "It's all nuts and bolts"

                          Mitch's Auto Service ctr


                          • #14
                            Every inch of this running chassis is because of you guys and that red book covered in grease and blood. Not done yet but glad I have a resource like you guys to help me through. Hopefully one day I can return the favor to another non mechanical person.


                            • #15
                              NOTE: Vince Falter emailed to tell me that :

                              10-34 NS taps are in fact equal to 5mm .75 (note this is a 10 34
                              NS special tap)

                              It seems the 10 34 "NS" tap is a special tap and NOT equal to the standard 10 34 NF

                              The castings I had trouble with MAY BE 10 34 NF... all I know is that they bind and squeak when installing 5mm .75 jets (both new and originals).

                              I will post more from Vince on this later. See post 18 for Vince's email

                              The following jets are 5mm .75 from the factory:

                              Comp jet (washer)
                              Idle jet (no washer)
                              Cap Jet (washer)
                              Main jet (one washer only)
                              GAV seat (washer) (Brass seat is not used on later carbs).
                              Idle air adjustment screw

                              10 34 is close but not correct (see below).

                              There are a couple of books out there that still list the incorrect 10 - 34 tap.

                              10 32 is way off. I never tried this size tap.

                              I do not know if the 5mm .75 jets will even thread into 10- 32 hole unless the jets are re-threaded with a 10-32 die maybe!.

                              If you try to thread a correct 5mm .75 jet into the casting and it binds up and makes a squeaking noise as you turn it then someone has threaded it with the incorrect 10 34 tap. If the hole is worn out and oversized then no squeaking ...

                              This can be corrected by rethreading with the 5mm .75 tap.

                              I have corrected a number of castings that have the 10-34 holes in the castings.
                              This problem is not just with 2 or 3 castings... but more like 30 or 40 castings...

                              Many were rebuilt by the same person as seen by the markings stamped on the carbs.
                              Last edited by benson; 06-03-2017, 06:28 AM.


                              • #16
                                Thank you!


                                • #17
                                  See note in red on post #15 above


                                  • #18
                                    There are three classifications of threads:

                                    NC = Coarse
                                    NF = Fine
                                    NS = Special

                                    Here is email from Vince that explains what is going on...

                                    Just some info for your consideration.

                                    I have researched the original Ford carburetor drawings at the Benson Ford Research Center.

                                    You may not believe it, but jets are 10-34 NS,
                                    not the standard 10-32 NF.

                                    10-34 NS is what is called for on the Ford drawings. It is special.

                                    That is a soft conversion from metric of 5mm by 0.75 pitch.
                                    They are equal.

                                    The jets were designed in metric by Zenith, but the Ford drawings are drafted in English.

                                    10-34 NS = 5 x 0.75 mm metric (which is also a special size in metric).

                                    The GAV Housing is 1/8-27 NPT. That is standard 1/8th inch pipe thread.

                                    The GAV Needle is 1/4-24 NS, which is a special size. It is not NPT as Beauford says.

                                    It is also not 1/4-20 NC or 1/4-28 NF which are the coarse and fine standard thread sizes.

                                    Vince Falter
                                    Last edited by benson; 06-02-2017, 10:03 PM.


                                    • Mitch
                                      Mitch commented
                                      Editing a comment
                                      Benson thanks for relaying the info!

                                  • #19
                                    I learned something today ... I always thought that the reason for the binding of jets and squeaking was the 10 34 tap size (not knowing that there are NC, NF and NS tap types ...

                                    Looks like it might have been because someone used a 10 34 NF tap instead of 10 34 NS!


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