How do I stop the brass GAV housing gasoline leak at carburetor?

[Pat Martone]

I can't seem to stop a gas leak where the brass GAV housing meets the carburetor.
I understand this is a common leak area because it is lower than the float level.
I have read about and tried using Teflon tape around the brass GAV housing's threads, but it still leaks gasoline.
Any other recommendations would be appreciated.
Thanks!

[Gary WA]

What type of carb do you have? Zenith? I've built many carbs but never had one leaking at that point??

[BILL WILLIAMSON]

Pat,
When you take the brass GAV housing out, does it have a TINY wire circlip around the pointy end?? Sometimes, when it is missing, it contributes to gas leaks. It's main purpose is to add friction so the GAV doesn't vibrate open or closed on it's own. You can squeeze the circlip to add tension. Do it in the middle of a BIG PLAIN towel so you don't lose it!! It's about this big-C-! Bill W.

[Pat Martone]

Yes, it is a Zenith carb.
Yes, the wire clip is there and mounted
properly.
I read somewhere that this was a common leak area.
I think the gas might be melting the Teflon tape, which is what this article suggested using.

[Ron in Quincy]

Try Permatex Avation Gasket Cement, a small amount, on the threads of the GAV housing before installing; it is gas resistant, also works well on the jet gaskets.

Ron

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There is an aircraft Teflon tape that is made for gasoline lines.

[Jazzjr]

Possible Gas Adjusting Valve Seat is Blocked with dirt or rust.
Gas Adjusting Valve is open too much or seat is not honed to let needle seal.
Zenith Carbs before 1929 had a removable Brass seat, all others after 1929 had the seat cast into the Housing. I have stopped one that was leaking using the Procedure below. You also need to run a tap, to clean out the threads for the housing, it may not be inserted enough. Gas Adjusting Valve (GAV) hole, in lower casting, has 1/8-27 NPT (Pipe) threads. Use caution not to cut threads deeper, as it is a pipe thread.

Gas Adjusting Valve Seat Honing Tool & Guide

• To obtain a good seat when Gas adjusting valve is closed, the seat sometimes needs to be polished to remove pits, dirt scratches, etc. This tool and guide provides a mating, aligned surface that can be spun against the seat with polishing compound on it. The tool is made by soldering two needles together back to back. The end that will go into the guide and provide the polishing surface needs to have its threads removed to enable it to be spun continuously with a drill. Using an old GAV housing, I've removed the spring to let the tool spin more freely. Some people also cut down both ends of the housing.

I borrowed the above from http://www.model-a.org/

[Joop]

Sometimes the carburetor housing is cracked as the brass housing is forced in to far.

[Gary WA]

Originally Posted by Pat Martone

Yes, it is a Zenith carb.
Yes, the wire clip is there and mounted
properly.
I read somewhere that this was a common leak area.
I think the gas might be melting the Teflon tape, which is what this article suggested using.

Make sure the gav is open when screwing in the outer case and the threads look good,sounds like its not screwed in tight,and make sure its clean. remove from carb to ensure nothing is down in the jet area seat?

[redmodelt]

Get some Permatex Thread Lock. It comes in a small white tube and works great for sealing the outside housing of the GVA.

[30ccpickup]

[Pat Martone]

Thank you all, for the informative replies!
I will investigate further.
I wonder where I can buy the 3 mentioned sealers that resist gasoline:

- Permatex aviation gasket cement, or

- Aircraft teflon tape, or

- Permatex thread lock?

(The only white Teflon tape I have is the regular Teflon tape used by plumbers for water pipes, which "melts" upon contact with gasoline.)

[mot]

i like Joops answer
with a pipe thread it is easy to tighten it too much, which will crack the casting
you have to really look close to see the crack
the thread sealant may help seal it

[Smurkey]

You can get any of those sealers at an auto parts store (NAPA, Autozone, etc).

[[email protected]]

Originally Posted by Pat Martone

Thank you all, for the informative replies!
I will investigate further.
I wonder where I can buy the 3 mentioned sealers that resist gasoline:

- Permatex aviation gasket cement, or

- Aircraft teflon tape, or

- Permatex thread lock?

(The only white Teflon tape I have is the regular Teflon tape used by plumbers for water pipes, which "melts" upon contact with gasoline.)

The aircraft Teflon tape I use is yellow in color and is sold at most Big Box harware building supply stores. I bought my last spool at a Farm and Fleet store and it was next to the white Teflon tape on the shelf.

[Mitch//pa]

i would ck with to high a float level or crack in the threads

[Marco Tahtaras]

It's a long shot but worth mentioning. I had that problem 17-18 years ago with a used adjusting needle housing that appeared to be perfect. I tried all the usual stuff short of gooping the heck out of everything which to me was not an acceptable solution. I bummed a NOS one from a buddy and the problem was gone. My "mint" used one did go in a little further but I never went back and determined the exact cause.

[Purdy Swoft]

I use High Tack made by Permatex. Bratton lists this product on page 36 of the 2012 catalog and calls it head gasket and gas line sealer. This product comes in a can with a handy brush applicator on the cap. Permatex high tack gasket sealer is gas resistant and can be found at parts houses that sell Permatex products. I have found that teflon tape can cause more problems than it solves, like cracked housings and stopped up needle valves.

If its not stalling when brakeing, the float level may be ok. Its a good chance that the lower housing of the carb has a small crack where the needle housing fits , caused by use of the teflon tape. If the housing is cracked, a good used lower housings can usually be found for a reasonable price. I got one from Berts

[modela-carb]

The earlier carbs had a carburetor adjusting needle seat that screws into the bottom of the adjusting needle housing (with a gasket). It looks like the comp jet but is a little larger. The adjusting needle seats into this to adjust the GAV. In Jan 1930, this piece was removed and an integral seat was installed in the carb. Occasionally, the needle seat is left out, or the gasket is not installed making it impossible to close down the GAV. I'd remove the needle housing, shine a light down the hole & see if your carb should have the needle seat but does not or if it has the integral seat. You might find a a solution short of chemical fixing.

[Pat Martone]

My carb and car runs great; engine never stalls when stopping at a light and it does not leak when the car is running. I see a very slight leak after the car has been parked for a day or so, with the fuel shut off. My carb was completely rebuilt and flow-checked by a reputable person last year. I will remove what's left of the melted Teflon tape on the GAV housing and try the recommended Permatex high-temp thread sealant. I am hoping that I don't have a cracked carburetor housing.
Thanks again for all the advice.