Zenith Carb Part Identification

J

james1savage

Member
Gents, I pulled apart my Zenith carburetor as I found that there was some small rust bits that found there way into it. Cleaned everything out and took it to a local shop to have the passages blown out with air to ensure they were clean.

When the mechanic put it back on the counter the piece of something in the following pictures I believe fell out of the lower casing. I'm wondering if it was pressed in somewhere, but it also looks beat up and/or broken.

Can anyone identify it? I've reviewed an exploded view of the Zenith and can't match it to a part.

Thank you in advance for any insight.
 

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Not a zenith carb part!
 

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If your carb is a 28-29 with threads in the bottom area of the GAV, then someone probably replaced the threaded brass fitting with the piece correctly identified by Ray in La Mesa.
 
Thanks gents. I’m going to put the carburetor back together leaving it out and see how things go. I’m not sure on the year of the carb as I bought it rebuilt.
 
Perhaps it is a piece of debris that was in the sandblasting cabinet? Perhaps it was debris that got into the carburetor from the shop? It is not a recognizable Zenith part.
 
Steve Schmauch said:
If your carb is a 28-29 with threads in the bottom area of the GAV, then someone probably replaced the threaded brass fitting with the piece correctly identified by Ray in La Mesa.
Click to expand...

I think you may have nailed it. Just finished putting the carburetor back together and started the engine. It immediately ran very rich and almost stuttering. I'm at 1 1/2 turns on the mixture screw and it barely caught up with air when I turned it 3+ turns out. I'm thinking the bottom area of the GAV is bigger than the needle now and letting too much fuel past.

Here is a picture of down the GAV shaft hole, looks like there's room for something plus the needle.

I'm thinking I should push it back down to the bottom area, but what are your thoughts?
 

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It’s difficult to tell by the photo but is the bottom of the GAV cavity machined with a hole that the needle would seat in or are there threads at the bottom where a brass seat and washer would thread in? It is probably just missing the seat but why they didn’t just put another one back in and used the wrong part is the mystery. Maybe the threads are stripped.
 
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The GAV seat which is threaded into the early castings is A-9532

FYI: Threads in casting and on A-9532 are 5MM .75.
 
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the shank of the GAV needle is 2.45 mm dia, Thus if the the hole in the casting is c2.4 mm dia or less it does not take the brass seat ( the hole measured 2.1mm on one of my carbs ). If the hole in the casting is 4.2mm it takes the brass seat ( or is exceptionally-never-seen-before worn !). Can't fathom mm into inches but I'm sure you can. I used the shanks of drills to measure the diameter of the hole.
 
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James1savage--Your photo looks like it has a threads meant for installing a brass GAV seat. It looks kind of like the brass jet located in a carburetor bowl. These parts are common and you should be able to find one at any A vendor. Installs with a narrow blade screw driver, but not ultra tight! The later carbs had a funnel-shaped hole in the cast iron, which eliminated the need for this brass GAV piece. You are correct in that it is nearly impossible to regulate gas-air mixture without a proper GAV seat.
 
The one on the Left takes a brass insert the one on the Right doesn't
 

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on each of the two photos Gav Brass seat insert on Left , Comp jet on Right
(Brass seat is longer, and deeper insert, and wider bore than comp jet)
 

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You fellas are great, thank you again for the knowledge. I sourced a GAV brass seat insert and it threaded right onto the spot. Everything back together and it runs great.

I greatly appreciate everyone's comments.
 
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