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Model A Zenith Carburetor

Ford Garage

Gas Adjusting Valve (GAV) Wrenches & Sockets

This is one of the service tools that Ford and KR Wilson forgot to make.

It is a special Williams 8021 13/32 inch hex wrench for removing and installing the original brass gas adjusting valve (GAV) housing in the Model A Ford Zenith carburetor lower cast iron body. These wrenches were also produced under the Armstrong name.

The Model A Zenith GAV housing and casting threads are 1/8-27 NPT pipe thread. Model B Zenith carburetors use a press-fit brass GAV housing into the iron casting, not a threaded style GAV housing.

On a related note, the inside threads of both the Model A and Model B GAV housings for the needle are also special. They are 1/4-24 UNS thread.

The difficulty with the original GAV housing design is that 13/32" is a extremely unusual tool size. Low profile deep well SAE sockets as well as box and open end wrenches in this size have not been readily available in the last 40-50 years.

There is very little clearance between the brass hex and the iron carburetor casting, making it difficult to remove or install the GAV housing without damage.

Open end wrenches do not have room to move and will round off the hex on a stubborn GAV. Typical box end wrenches will not fit in the space available to the casting.

This handy 6 point 13/32 inch wrench shown above is one of a limited number made and sold by Rob Mills many years ago and it also works great.

In addition to wrenches, this excellent 13/32 inch 12 point socket shown above and below was produced in 1/4" drive by Snap-on Tools years ago specifically for the Zenith carburetor GAV, and was part of their series of carburetor service tools.

For Sale:
These 13/32 inch Williams wrenches and Snap-on sockets have been out of production for many years now, but I often have a couple of nice used ones available for sale for $30 each for the wrench, and $25 each for the socket (socket only, not including T-handle).

More related information on Ford Garage:

  1. For more Model A & B related information, use the Site Search box at the top or bottom of this page.
  2. Model A Zenith Carburetor Theory of Operation
  3. Model A Zenith Carburetor Numbering
  4. Model A & B Carburetor Jet Sizes & Flow Rates
  5. Model A Carburetor Float Mass
  6. Model A Zenith Carburetor A-9545 Secondary Well Variations

May 2001