The Ford Barn

Marshall V. Daut · 05-11-2015, 06:56 PM

I already went through the archives to find an answer to my question and although there's lots of good information about the Model A Zenith carburetors, no thread supplied me with what I need to know. I also checked the standard Model A carburetor books and only the Rex Reheis book came close to answering my question. Close, but no cigar. So, here goes.
For years when I went through Model A carbs, only rarely did the passageway plugs need to be drilled out and the passageways cleaned. Straight-forward stuff, especially since the brass plugs to seal the holes have become available. But a friend's Zenith 2 carb has the angled passageway in the lower casting from the cap jet to the GAV area (or vice-versa, depending upon your viewpoint). I have never encountered any Zenith carbs that didn't have the short, straight entry to the secondary well from the side. The original brass plug that was in place was parallel to the body, meaning it was not angled towards the cap jet, down the raised passageway (see photo). I see no hole from the drilled plug down this passageway to the cap jet, although the cleaning bit does go clear through
to the secondary well. I assume that because of this raised passageway between the cap jet and the GAV, it needs to be cleaned out, too? In the accompanying photo, this would be from "A" to "B". I wonder if the crud is so dense that it is blocking the passageway opening to the cap jet?
So, my question is: do I need to carefully drill in-line down this passageway between "A" and "B"?
Thanks in advance, you Zenith carb gurus, who have gone through this song and dance.
Marshall

Benson · 05-11-2015, 08:48 PM

Marshall,

There are two ways that the port goes from GAV (point A) in your photo.

1. One goes to the secondary well.

2. One goes to the cap jet.

3. Now if you push (do not drill this passage just use the bit to see the passage) a drill bit into the comp jet from the bowl, through the secondary well and on into the CAP jet, this is ONE way to connect them. (most common)

4. If the drill bit stops at the secondary well ... there are two ways that I know of that Zenith connected to the CAP jet.

1. One is a brass plug at point B on your photo.

2. The second is directly behind your "B" (to the right in photo) on the opposite side of the boss. Check for a brass plug on BOTH sides.

If your carb has the EXTRA brass plug on bottom it is either

1. Mid 28 to end of 28 (from memory so do not quote me.)

2. OR - early 29 to mid 29.

One has extra plug on front of boss and the other has plug on back of the "BOSS".

I do not have a examples of the three types of carbs here to check this for sure as I am not at the shop.

NOTE:The passage that connects the cap jet to the secondary well comes into secondary well from above the one that goes out the opposite way to the COMP jet. This is why you can not get the drill to go through the COMP jet and through the secondary well to the CAP jet.

Like you I do not like to drill plugs only last resort! Too much chance of damage.

I have used MIG wire ( stiff steel wire) and needle nose to push through these passages, then bead blast to clear passages.

Take it easy with sand or media blasting of threaded holes ... the threads can be easily destroyed

Tom Endy · 05-11-2015, 08:59 PM

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Marshall:

My advice is to never drill the passage plugs out. The new plugs may not fit properly, if too large they will crack the casting going in. If too small they will fall out. You may also end up drilling through something, like the throat of the carburetor.

I have encountered the early castings you speak of and believe it or not I can get a paper clip through the passageway. Start at the cap jet end. With a small lite locate the passage at the bottom of the boss and put enough English on the paper clip to worry it through. All the passageways can be cleaned out with a paper clip, even the one in the throat. However there is not need to run this one as a blast of shop air pointed into where the idle jet screws in will tell you it is open. Put your finger over the small hole in the throat when giving it a blast.

Go to the tech library for the Santa Anita A's, there is a Zenith article explaining the paper clip maneuvering.

Tom Endy

05-11-2015, 08:48 PM	#2
Benson Senior Member Join Date: May 2010 Posts: 2,594	Re: Drilling out Zenith passageway plugs Q. Marshall, There are two ways that the port goes from GAV (point A) in your photo. 1. One goes to the secondary well. 2. One goes to the cap jet. 3. Now if you push (do not drill this passage just use the bit to see the passage) a drill bit into the comp jet from the bowl, through the secondary well and on into the CAP jet, this is ONE way to connect them. (most common) 4. If the drill bit stops at the secondary well ... there are two ways that I know of that Zenith connected to the CAP jet. 1. One is a brass plug at point B on your photo. 2. The second is directly behind your "B" (to the right in photo) on the opposite side of the boss. Check for a brass plug on BOTH sides. If your carb has the EXTRA brass plug on bottom it is either 1. Mid 28 to end of 28 (from memory so do not quote me.) 2. OR - early 29 to mid 29. One has extra plug on front of boss and the other has plug on back of the "BOSS". I do not have a examples of the three types of carbs here to check this for sure as I am not at the shop. NOTE:The passage that connects the cap jet to the secondary well comes into secondary well from above the one that goes out the opposite way to the COMP jet. This is why you can not get the drill to go through the COMP jet and through the secondary well to the CAP jet. Like you I do not like to drill plugs only last resort! Too much chance of damage. I have used MIG wire ( stiff steel wire) and needle nose to push through these passages, then bead blast to clear passages. Take it easy with sand or media blasting of threaded holes ... the threads can be easily destroyed Last edited by Benson; 05-11-2015 at 09:21 PM. Reason: I edited this post quite alot so you might want to re-read it

05-11-2015, 08:59 PM	#3
Tom Endy Senior Member Join Date: May 2010 Location: Southern California Posts: 3,131	Re: Drilling out Zenith passageway plugs Q. Sponsored Links (Register now to hide all advertisements) Marshall: My advice is to never drill the passage plugs out. The new plugs may not fit properly, if too large they will crack the casting going in. If too small they will fall out. You may also end up drilling through something, like the throat of the carburetor. I have encountered the early castings you speak of and believe it or not I can get a paper clip through the passageway. Start at the cap jet end. With a small lite locate the passage at the bottom of the boss and put enough English on the paper clip to worry it through. All the passageways can be cleaned out with a paper clip, even the one in the throat. However there is not need to run this one as a blast of shop air pointed into where the idle jet screws in will tell you it is open. Put your finger over the small hole in the throat when giving it a blast. Go to the tech library for the Santa Anita A's, there is a Zenith article explaining the paper clip maneuvering. Tom Endy