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Old 09-16-2020, 08:57 PM   #1
Bob Johnson
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Default Carb leak

I am getting a drip out of the back end of the carburetor when the fuel valve under the tank is open. Here is the weird part. I have tried 3 different carburetors and six different float jets. I have added way to many shims under the float jet. I have installed a "J" tube at the drain plug. With two of the carburetors the gas level would initially stop at the correct level. Then it would slowly rise until it was high enough to push gas out through the main jet. The third carburetor is a side bowl with the side bowl removed. In this case the gas level stops below the correct level and stays there. However it still leaks. This car sat for 30 years with not gas in the tank. Could be sediment. I did install a micro filter in the tank above the fuel valve. Below a picture of the side bowl carburetor with the "J" tube showing the fuel level in the bowl.



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Old 09-16-2020, 09:26 PM   #2
Brentwood Bob
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Default Re: Carb leak

Fuel valve suspected.
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Old 09-16-2020, 11:20 PM   #3
Chuck Sea/Tac
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Default Re: Carb leak

I’m unclear where the leak is exactly? Front end? End of carb Facing front of car?
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Old 09-17-2020, 12:19 AM   #4
Bob Johnson
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Default Re: Carb leak

It is leaking out of the back of the carburetor where the air enters.
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Old 09-17-2020, 02:27 AM   #5
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Default Re: Carb leak

If you're sure it leaks from the air intake with the fuel level as in your pic I suspect the main or cap gasket. But whatever it's one of the list below! ..
Possible leaks from Zeniths
Problem: Remedy
1 Leaking/loose float valve gasket: Tighten/reseal/replace
2 Leaking float valve: (or crud stopping it sealing)Replace ( or clean up if possible )
3 Friction on float hinge: Loosen
4 Incorrectly set fuel level: Re-set
5 Hole in float: Repair or replace
6 Too many gaskets on main jet Check
7 Cap jet or main jet too short: Replace
8 Leaking/loose gasket at main jet: Tighten/reseal/ replace
9 Leaking /loose gasket at cap jet: Tighten/replace
10 Leaking or loose GAV housing threads: Tighten/ reseal/ replace
11 Leak at fuel inlet union: Tighten/reseal/replace
12 Loose/leaking gasket at strainer: Tighten/reseal/replace
13 Loose/leaking gasket at drain plug: Tighten/reseal/replace
14 Cracked housing/leaking passage plugs: Repair or replace

1-7 will generally manifest as poor running.
8-14 will generally not affect running unless there is excessive leaking.
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Old 09-17-2020, 02:44 AM   #6
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What stumps me is I tried 3 different carburetors and all 3 leaked. I also tried 6 different float valves and all leaked. I think I will install the carburetors on a different car and see what happens.
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Old 09-17-2020, 03:10 AM   #7
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Default Re: Carb leak

yes, puzzling. Are you sure it's not seepage from the inlet union ? If the fuel level in the pic is not rising then that float valve is certainly working OK . Sometimes the leak is hard to locate. eg fuel always trickles down to the lowest point ( the drain plug) and then drips so the drain plug is often blamed but rarely the the culprit
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Old 09-17-2020, 12:20 PM   #8
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Default Re: Carb leak

Did you use the same fuel line?
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Old 09-17-2020, 12:47 PM   #9
Ernie Vitucci
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Default Re: Carb leak

Good Morning...Many Model A Zenith Carburetors have a tendency to dribble a bit. Many of us find that they don't leak when the engine is running, only after it stops. We tend to close the gas valve when we shut off the engine and run the engine for a minute or so and then shut it down.

Another problem can be that the valve on the bottom of the tank does not shut off completely and so the head pressure of the gas in the tank will work its way to the carburetor and finally move fuel past the float valve, even if closed. Sometimes the answer is the modern quarter turn float valve system sold by Bratton's. You might look it up and see what you think...some of us dribble and we're not quite as old as our cars! Ernie in Arizona
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Old 09-17-2020, 01:48 PM   #10
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Default Re: Carb leak

Quote:
Originally Posted by Ernie Vitucci View Post
Good Morning...Many Model A Zenith Carburetors have a tendency to dribble a bit. Many of us find that they don't leak when the engine is running, only after it stops. We tend to close the gas valve when we shut off the engine and run the engine for a minute or so and then shut it down.

Another problem can be that the valve on the bottom of the tank does not shut off completely and so the head pressure of the gas in the tank will work its way to the carburetor and finally move fuel past the float valve, even if closed. Sometimes the answer is the modern quarter turn float valve system sold by Bratton's. You might look it up and see what you think...some of us dribble and we're not quite as old as our cars! Ernie in Arizona
I agree 100% with what Ernie wrote (except maybe me dribbling!). I had a carb drip that was driving me nuts. I finally replaced the main S/O valve even tho it didn't seem to be leaking while I was watching it. But by morning I would have drips on the engine pan (and the catch can I placed under the car). New valve from Snyder's worked.
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Old 09-17-2020, 02:26 PM   #11
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Default Re: Carb leak

I had same problem... installed a quarter turn shut off from Brattons and solved my problem (part # 13350)

Last edited by PG31A; 09-17-2020 at 02:35 PM.
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Old 09-17-2020, 07:31 PM   #12
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Default Re: Carb leak

Had the smell of gas in the garage after the 31 was parked overnight with the Shut Off valve closed. Finally disconnected the fuel line at the carb and stuck it in an empty bottle overnight. Next morning had about two oz. in the bottle. Changed the Shut Off valve with a new one from Bratton's and the problem was fixed. The Zeniths tend to drip overnight if the valve is open or leaking - common problem. Went through a few inlet valves in the carb to try and stop the leak with minor success. Had the best luck with a viton tipped valve which leaked at first but eventually took a set and leaked very little. Let us know how you fixed the problem.
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Old 09-17-2020, 07:46 PM   #13
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Default Re: Carb leak

Quote:
Originally Posted by PG31A View Post
I had same problem... installed a quarter turn shut off from Brattons and solved my problem (part # 13350)
Quote:
Sometimes the answer is the modern quarter turn float valve system sold by Bratton's.
That's not a float valve.
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Old 09-18-2020, 07:49 AM   #14
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Default Re: Carb leak

With a good needle valve, properly adjusted float, and a good shut off valve you can still get a carb drip out of the air inlet. In my experience, it is almost always bad gaskets (fiber washer) on the Main Jet, or the Cap Jet. If that is the case, even with a good shut off valve, it will drip until the float bowl is empty.

Inspect and clean up the mating surfaces and replace those gaskets. Get them good and snug, but be careful not to over-tighten them.

In rare cases the Main Jet or Cap Jet can be too short. I'm not sure how this happens, but I have seen it. If either is below the float level, even with a good shut off valve, it will drip until the level in the float bowl is below the top of those jets. The only way to correct this is to replace them with the proper length...just buy new ones from a reliable supplier. (As a temporary fix you can lower the float level below the top of those jets.)

I hope this is helpful.

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Old 09-18-2020, 10:55 AM   #15
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Default Re: Carb leak

Quote:
Originally Posted by KGBnut View Post
With a good needle valve, properly adjusted float, and a good shut off valve you can still get a carb drip out of the air inlet. In my experience, it is almost always bad gaskets (fiber washer) on the Main Jet, or the Cap Jet. If that is the case, even with a good shut off valve, it will drip until the float bowl is empty.

I'd add the float valve gaskets to that suspect list, especially if you're using more than one to set the float height.
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Old 09-19-2020, 03:29 AM   #16
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Default Re: Carb leak

It's not the float valve or the float valve gaskets that's the leaking issue in post #1... it says ".... In this case the gas level stops below the correct level and stays there. However it still leaks..."

Last edited by johnbuckley; 09-19-2020 at 12:00 PM.
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Old 09-19-2020, 06:39 AM   #17
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Default Re: Carb leak

I couldn’t see the picture until now. Maybe it’s an illusion but the fuel level looks too high? What level are you setting it at?
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Old 09-19-2020, 11:44 AM   #18
Bob Johnson
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Default Re: Carb leak

I put one of the carburetors on a different car and it did not leak. So I do not think it is a problem with the any of the carburetors. Also the gas shut off under the tank is not the problem. As I said previously it only leaks when the gas shut off valve is open. Yes if I just shut off the valve I would not have a leak. However there should not be a leak even if the valve is open. As I said previously this car had sat for years in storage. I did install a micro filter in the gas tank but my guess is that there are very small particles getting to the carburetor and preventing the float valve from closing all the way.



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Old 09-19-2020, 12:08 PM   #19
Brentwood Bob
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Default Re: Carb leak

Makes sense. I would flush the tank, or consider derusting. With the micro screen in the tank you are not seeing everything. Got a similiar problem with a permatex coated tank and deteriorated fuel. PITA.
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