Heads Up...Restorer carburetor article error

[pat in Santa Cruz]

The recent Restorer, vol58, issue 4, has an article on honing the Zenith seat. There is an error in step 3, chase threads. It says the thread tap to use is a 1/4-18 pipe tap. It is not. The correct tap is a 1/2-20.

[Tom Endy]

I believe you are correct. My experience has been that the taps used on a Zenith carburetor are the following:

3\8-24
Housing bolt (holds the two halves together)
Secondary well
Drain plug

1\2-20
Float valve
Filter assembly
Fuel inlet

5\16-18
Flange mounting bolts


1\8-27 pipe thread
GAV assembly only

5mm-75 pitch
main jet
cap jet
comp jet
Brass GAV seat (early Zenith's)

The idle jet is a small pipe thread, it does not take the 55mm-75 pitch. I do not know the size.


I had not caught the thread size discrepancy, but I did notice he is calling out a Dremel stone, part number 952. I read somewhere that the Dremel part number was 911 (easy to remember). I had to order them on line as they were not available locally. They were inexpensive so I ordered six and gave a few away. They seem to fit the taper properly and I have used them with good success on badly pitted fuel inlets. His 952 call-out may also be correct.

I am sure it was an oversight, the author surely knows the fuel inlet is not a pipe thread. I am surprised the "committee" didn't catch it.

When you submit an article to Jim Spawn, the editor of the Restorer, he puts it in the proper format then sends it back to you for your approval. At the same time MAFCA requires him to send it to the "committee". A good idea actually, they have reviewed the last few articles I have had published in the Restorer. The committee includes the MAFCA technical director, publications director, Les Andres, and I believe the MAFCA members of the Judging Standards committee. The tap size must have slipped past them. Easy to do.

Tom Endy

[Carb Guy]

Tom Endy. Rex Rehis says the idle jet is a 55mm 75 pitch and. I have found that to be the case and always retap the same as the other jets. Dick H.

[Drive Shaft Dave]

I think the 55mm dimension is incorrect, more like 5.5 mm .

[5window]

Originally Posted by Drive Shaft Dave

I think the 55mm dimension is incorrect, more like 5.5 mm .

55mm=2.2" so I think you are correct that that is a typo. I used to do all of my prescription dosing at work in my head-I always do it twice with a calculator now as well. Mistakes can be costly.

[Carb Guy]

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Typo Yes. Should have been 5mm-75 pitch, that is the size listed in Bratton's catalog.

[pat in Santa Cruz]

the following correction is posted on the MAFCA website:

Restorer magazine Correction

November 5 - There is an error in the Honing Zenith Fuel Inlet Seat article by Lynn Sondenaa in the November/December Restorer magazine. A local Model A owner pointed out that the tap being used to clean out the threads of the fuel inlet on the Zenith carburetor shown in the article is not the correct size.
Step 3 on page 8 says to use a 1/4-18 pipe tap, and Figure 7 on page 9 clearly shows that tap in place. The correct thread size for that inlet is 1/2-20 National Fine. It's suggested t that you put a small post-it-note on that page with the correct information so it will remind you in the future of the error.
-- Chuck Christensen, 2013 Technical Director