Marvel-Schebler Carburetor Hex vs. Slotted GAV

leo

leo

Well-known member
Most of the GAV parts on the Marvel-Schebler carburetors are hex I'm told with few being slotted (keyed). Why is that if these were sold as Model A Ford replacement?
 
We've been having a discussion regarding the difference. Seemingly NO difference - except for the slot instead of the hex.

Those slotted version I've seen on Ebay (I don't own one myself) seem to be is pretty good to very good condition. Most of the hex version (the majority of those seen) seem a little worse for wear. It could be that the slot version was the "last" design evolution/improvment of the Allstate carb?

Either of these were the same carb (essentially) with only minor other differences. And all sold as replacement for the Model A Zenith.

Joe K
 
OK, but I don't get how you can use the un-slotted version on a Model A. Did they sell each carburetor with both types of GAV stems?
 
I went back through all the old posts for Marvel-Schebler carburetors and it appears that they all had the hex type of GAV. Don't know what the work around was but I bet someone out there does!
 
I'm glad you started this thread. First you ask how the hex or slotted versions could be used on the model A. These carburetors came with their own needle driver that connected to the choke rod just like the Zenith. If you notice the choke connection on the Marvel you will see that the slotted driver connection is the same.

I was just out in the shop and discovered that a Zenith needle housing and needle will thread right in to the Marvel housing without any modification. It screwed right in place and tightened up good with a 7/16 open end wrench. It seems that needle length will work out when the whole needle and housing are used .This would allow the use of the common Zenith-Tillotson style needle driver. I haven't tried it on a car but figure what have you got to lose if you've got a Marvel that you can't use because some of the parts like the needle driver is missing . This should be a bolt on swap for the whole GAV assembly.

If you notice the front carb has a hex needle, the rear carb has what we think is the later round grooved needle. I will try and post a picture of a Marvel with the Zenitn GAV installed later this evening. Swort research !!!!!!!

4870835-T400300.jpg
 
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Hey Purdy, thank you for your input. I guess over the years the needle drivers that connected to the choke rod must have become lost or scarce because the only way you can get one is to find a used carburetor with one on it......
 
Leo, you are correct. many times when the needle driver was lost or missing the carb was considered a parts carb and never used. Here is the picture that I promised. the Marvel to the right has the complete Zenith GAV assy installed. It screwed right in and tightened up nicely The needle adjusts and bottoms same as the original GAV. The carb on the left is a normal Marvel and the dissassembled Marvel GAV assy that was removed from the front carb is pictured below.

4899334-T400300.jpg
 
Thanks Jesse, I hoped you would see this. I just had to try and see if the Zenith GAV assembly would fit without modifications and it did !!! Maybe this will help save a few Marvel carbs with missing parts. If one Marvel carburetor runs good, two will run better. I actually get better gas mileage on my roadster with two B carbs than I do on my tudor with one side bowl Zenith.
 
Please detail the procedure for installing the Zenith GAV assembly on a Marvel carburetor which has it missing. What parts are needed from both the Marvel and Zenith? Are the Zenith parts available from the dealers?
 
The procedure is a simple bolt on. No mods to the Marvel carburetor was needed. The parts are available from any of the model A parts dealers. I will use Snyders as a referance as they use original parts numbers. Page A-142 in the new catalog , .adjusting needle , part number A-9525 price $4.70 , adjustment needle housing, part number A-9528 Price $7.60 and Driver part number A-9570-CP price $10.25. Many model A guys .will already have these parts on hand either used or new. Just remove the old GAV assembly from the Marvel carb, nut and all as pictured above in my post #7 . Install the adjustment housing, it just screws in place . Some need a 7/16 wrench or deep socket to replace others are 13/32. The other Zenith parts listed above install as normal It is a simple remove and replace bolt on. I haven't road tested mine yet. Triumphleroy says in post #8 that he is running this setup on his sport coupe and it runs good. The Marvel Carbs are light weight and should be a good choice for the Vortex manifold. The Marvel carb is a simple design that performs well. The main problem is that most Marvel carbs are older than me and missing parts. Stripped threads and warpage at the flange is another problem that can be repaired with thread serts and a little filing-sanding to flatten the mounting flange.
 
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There was also a post about some type of felt gasket on the adjusting needle to keep gas from leaking out for the Marvel?
 
None of my Marvel carbs had a felt washer on the adjusting needle, not even the one that I run on my 29 strip down. This is just a thought that I hoped would be interesting to some with Marvel carbs with missing parts. Sorry, I can make NO garuntee that everybody will have the same results as I did. It should be a simple bolt on improvement in most cases. Smiley face.
 
A gasket should not be needed with the Model A GAV bushing adapted to a Marvel Carb. The Model A GAV has an "extension" (tube) that extends above the gas level in the carb, and thereby spillage can't (well doesn't) occur.

So in a way, a Model A GAV and bushing are an "improvement" on the Marvel setup. The original little fiber gaskets to answer to perceived need (well by somebody) are a way to make the seal, but physics (fluids seek their own level) works better and more reliably.

Joe K
 
My thoughts as well, Joe . The Zenith carbs don't leak gas around where the needle housing attaches unless the cast iron is cracked. The zenith needle is shaped the same and seems to bottom in the housing seat as it should when the GAV is closed. The Zenith - Tillotson style GAV assembly is a bolt on for the Marvel carb as well.
 
Here's my report on M-S GAV situation.

1b41dcf8-3ba5-4fac-abbf-92e91737596f.jpg


The left carburetor above I removed the GAV and the pieces came out as you see them left to right. Not shown, but pertinent, is a fibrous washer found (and left) next in line to the right of the spring. Also not found a brass washer.

The existence of this fibrous washer I doubted at first, but probing around a bit with a small paperclip found a smaller recess/shoulder which the fibrous washer sits into. The spring is a slightly larger diameter than the fibrous washer and sits on the shoulder so formed.

I tried to remove the fibrous washer with the paperclip, using it like a pick, but the paperclip bends too easily and the fibrous washer is too firmly planted to allow easy removal.

The right hand M-S had the same parts but instead of the fibrous washer, it has a brass washer right-most in line, which could not be removed with the paperclip. Not sure what, if anything is below the brass washer.

Both of these Carbs are Hex GAV needles, I was not surprised to find a pair of knobs cast into the side of the aluminum/pot metal GAV Hex driver. This seemingly the placement point for a pin used to drive the the slotted GAV should it be required. So it seems one GAV driver pattern was drilled, hex'ed, or set up appropriate for it's GAV needle.

Heh. The left-most Carb holds fond memories of Amherst, NH. This the infamous (now) $3 carburetor. The right-most carb came on a basketcase AA truck which I disassembled for parts.

Joe K
 
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This is all good information. I have just installed a Marvel carburetor on my speedster and will be trying it out soon. While cleaning the carb I found a dried out fibrous gasket/packing at the bottom of the GAV well. I am now assuming that the purpose of the spring and washer are to hold the gasket in place since they seem to have no other effect. I saw on Renner's web site that they now include a GAV seal in their Marvel rebuild kit. I did not have a GAV driver so I made my own. All outside dimensions were copied from a Zenith driver. I made the hex by pressing in an aluminum insert and then drilling and broaching it out. The broaching tool was made using a hard hex wrench. I cut one point at a time using the indexing holes on my lathe to space them evenly. Thanks for all the information. I will report back on how the Marvel works out. Howie
 
Renner's Corner Model A Parts sell rebuild kits for the Marvel carburetors and it also says they sell individual parts from the kit too.
 
I just tried out the Marvel carburetor for the first time. I made my own gaskets to fit the GAV needle. I made a thicker washer to hold it in place. It did leak a bit so I added a second gasket under the washer which cured the leak. The engine started easily and ran good with minimal adjustment. I had to run the GAV about a half turn open to keep it smooth. It did run a bit hotter than I like so I,m guessing that was a bit lean. Will leave it open a bit more the next time. Now if the plugs stay cleaner and the fuel mileage improves I will be really happy. Thanks for all the input. Howie
 
For someone with a leak around the Marvel GAV, would it be better to get a GAV washer kit from Renners or replace the whole GAV assembly with the Zenith parts? Seems like a cheap investment either way (nice to have those).

-Blake
 
The Ford released Marvels were ALL identical and ALL had a hex shafted GAV needle with a straight threaded GAV nut into the body of the lower casting, if you have anything other than this it was sold by some other company like Western Auto or PepBoys. I make or have ANY part you could want for the Ford released Marvels 1-734-428-8424 Renner’s Corner.
 
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