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Old 10-09-2020, 08:42 AM   #1
dougar
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Default Zenith Carb Leak Puzzle

Iím a Model A newbie and have just joined this forum; apparently with my new-to-me 1931 Coupe, Iíve also joined the leaking carburetor club. Iíve been doing a lot of reading in this forum and recommended files online, but I am stumped. Sorry this post is so long.

BOTTOM LINE UP FRONT: Biggest problem is that gas seems to be coming out of the fuel bowl vent and/or the idle jet & compensator well vent on the engine block side of the carb. With a small mirror and bright light, I can see the wetness running down that side of the lower casting. Eventually a few drops per day come off the body bolt.

BACKGROUND: I bought Les Andrews' book, replaced the supply line & fittings, installed a new fuel shut-off valve under the tank with pencil screen filter, cleaned/rebuilt the cast-iron sediment bowl on the firewall, and rebuilt the carb. In the carb:
(a) I took a brand-new Viton-type float valve apart and cleaned off any obvious burrs on the internal edges of the brass housing and needle.
(b) Float itself was checked (no bubbles in hot water, correct weight, hinge is not bent).
(c) I believe the main and cap jets are the right height, although initially there was dampness in the air inlet. I believe this was due to the main jet and/or cap jet gaskets leaking so I tightened them, twice.
(d) I used a float-level visualization kit to be sure the fuel level is 5/8" below the upper gasket surface. When I first reassembled the carb, the level slowly rose and then gas came out of the vents at a fairly high rate Ė like a drop a minute. I found out that the new gaskets on the float needle valve were not sealing. Re-tightened, and the level held.

PUZZLE #1: I left the float-level visualization kit in place for a day or two. The level clearly held at 5/8", but after a while, gas was weeping out of one or both of the vents, resulting in a couple drips a day. As a test, I re-installed the drain plug, drove the car, turned off the fuel shut-off valve, and just let the engine die. No "leak" wetness below the vents initially overnight, but eventually it was obvious the next day. Is it possible for gas to creep up the wall inside the bowl or up the idle & compensator cavity and come out the vents?

PUZZLE #2: After sitting for several days, gas began dripping (although slowly) from the air inlet drain hole, too. That stopped, but thereís still dampness in the inlet. And of course the couple drops a day originating from the fuel bowl vent and/or the idle jet & compensator well vent continues. Am I back to square one?

Thanks in advance for your time and thoughts.

Doug Rohn
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Old 10-09-2020, 09:14 AM   #2
aford193031
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Default Re: Zenith Carb Leak Puzzle

I am sure others will jump in but I have read in other posts to leave the car running and then shut off the fuel valve. This uses the fuel out of the bowl. This ensures no carb leaks.
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Old 10-09-2020, 09:50 AM   #3
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Default Re: Zenith Carb Leak Puzzle

You could remove the lower half of the carburetor drain and dry it, fill the bowl to the proper level, letting it set over night to see if the fuel creeps and or leaking from the jets.
This week I've been looking for info on B zenith carb rebuild and I run across info that Ford recommended turning off the fuel. If turning off the fuel you still have a leaking problem, you need to repair the fuel valve. Also when you turn off the fuel valve and run it dry the carburetor will still have fuel in it along with fuel in sediment bowls which could weep into your carburetor.
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Old 10-09-2020, 11:25 AM   #4
Brentwood Bob
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Default Re: Zenith Carb Leak Puzzle

An extra gasket under the main jet can do what you describe. Dropping the level in the bowl would also help.
I have also had several castings, after derusting soaking expose a casting defect, and a crack.
The simple things sometimes are the challenge.
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Old 10-09-2020, 07:32 PM   #5
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Default Re: Zenith Carb Leak Puzzle

With a good shut off valve there shold be no dripping at all. Recommend disconnecting the fuel line at the carb and placing the end in an empty bottle for a period of time. If any gas collects in the bottle it would indicate the shut off valve is not completely effective. A very slow leak in shut off valves (even new ones) is not that unusual. My valve was leaking about two oz. overnight - just enough to allow the carb to leak and leave fumes in the garage. A new valve from Bratton's fixed my problem.
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Old 10-09-2020, 07:45 PM   #6
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Default Re: Zenith Carb Leak Puzzle

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I agree replacing the shut off valve
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Old 10-09-2020, 08:07 PM   #7
doa44green
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Default Re: Zenith Carb Leak Puzzle

My '31 wicks up the inner carb bowl wall and runs out at the gasket surface. I have not found anyone to help me solve this so I just live with it. I installed a ball type shut off valve at the tank. It does not leak!
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Old 10-09-2020, 08:33 PM   #8
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Default Re: Zenith Carb Leak Puzzle

The height of the jets can contribute, if they are too short, i.e. below the fuel level. If the jets do not have a concave surface, they can also leak via capillary action. I had one that was that way and I drilled it a bit to provide a concave rather than convex surface.
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Old 10-09-2020, 09:34 PM   #9
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Default Re: Zenith Carb Leak Puzzle

My experience with a leaky carburetor is on going. I think I have tried every one of the float shut off valves offered by the parts suppliers. I have not found one that works 100% of the time. The float valve is the primary cause for a leaky Zenith. Sometimes it works perfect then it will leak. It even will leak sometimes with the gas shut off. I am presently adding some Marvel Mystery oil to the gas as a way of providing some lubrication to the valve. It seems to have reduced leaking but still not 100%.
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Old 10-09-2020, 10:02 PM   #10
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Default Re: Zenith Carb Leak Puzzle

I've been battling the dreaded "drip" for a year. 2 different carburetors, first a Tillotson and now a Zenith 2. Three shut-off valves. Shims in the carb, etc. Cold weather is worse than hot. When I'm done for the day I run the carburetor almost dry and that seems to help. Ultimately the problem is the shut-off valve leaking. If it shut off the fuel to the carburetor, the carburetor couldn't leak. I'm considering a different style shut-off valve placed between the sediment bowl and carburetor. Maybe right at the output of the sediment bowl. Just haven't found the correct valve for the project.

PS, Mine drips from the air intake side. Comes out there and travels back to the lowest bolt on the bottom of the body.
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Old 10-10-2020, 05:42 AM   #11
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Default Re: Zenith Carb Leak Puzzle

It’s safe practice to turn the gas valve off after use but the carb should not leak if you leave it on. Your float valve seams to be leaking. Use a good original steel valve. Your problem is probably the valve gaskets are junk and leaking. How many are you using?
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Old 10-10-2020, 09:04 AM   #12
30 Closed Cab PU
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Default Re: Zenith Carb Leak Puzzle

Here is previous string https://www.fordbarn.com/forum/showt...lb+fuel+filter
If you do a search - tons more strings on this common subject.

Here is a good site about carbs https://www.modela.org/index.html

If replacing the shutoff valve install a pencil filter in it, trash/rust/grit in the gas tank can quickly ruin a shut off valve since the trash will gouge the shutoff valve inner workings.

Carb shim washers - do not use plastic shim washers or use plastic washers under the jets, plastic does not seal well, use fiber washers.

Jets - if replacing use flow tested jets, Renner's Corner is a good source.
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Old 10-10-2020, 09:28 AM   #13
Ed in Maine
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Default Re: Zenith Carb Leak Puzzle

A leaking carb is a real pain. I purchased the carb rebuild manuals written by Steve Pargeter and Russ Reheis/Gordon Biggar. They are an excellent addition to your library. The one thing that hasn't been mentioned yet that is in these manuals is that the gas level adjustment does not have to be 5/8 in. below the machined surface of the upper casting. This is the published, recommended level but it does put the gas level in the carb right at the tips of the Main and Cap Jets. If the gas is wicking out these jets because of high level, your garage is going to smell. I have found that usually two gaskets are required under the float valve to get a level a bit lower or 11/16 in. to 3/4 in. You are running a risk of stalling at stop signs if the gas in the bowl moves forward in the bowl and uncovers the Compensator Jet in the bowl. But if you are having a persistent problem, try lowering the level.
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Old 10-10-2020, 04:38 PM   #14
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Default Re: Zenith Carb Leak Puzzle

I have tried the viton tipped needle and seat with no success,took it apart and checked for debris shimmed it up and down carb still leaked.I installed original type needle and seat no leaks.
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Old 10-10-2020, 04:44 PM   #15
Fred K OR
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Default Re: Zenith Carb Leak Puzzle

Buy another used carb on line and rebuild it. May sole the problem and give you experience in the rebuild process. Buy new parts to put in for the rebuild.
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Old 10-12-2020, 09:54 AM   #16
dougar
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Default Re: Zenith Carb Leak Puzzle

Thanks, all, for the advice and commiseration. I've quoted a few of your responses below for comments and followup questions.


Quote:
Originally Posted by Big hammer View Post
You could remove the lower half of the carburetor drain and dry it, fill the bowl to the proper level, letting it set over night to see if the fuel creeps and or leaking from the jets.
This might be my next step in nailing down the problem.

Then, I need to put the fuel level sight gauge back on to see if the level is still holding at 5/8".

Quote:
Originally Posted by Brentwood Bob View Post
An extra gasket under the main jet can do what you describe. Dropping the level in the bowl would also help.
I have also had several castings, after derusting soaking expose a casting defect, and a crack.
The simple things sometimes are the challenge.
I'm sure it is something simple, just trying to figure out what. Pretty sure there is only one gasket under the main jet.


Quote:
Originally Posted by Mulletwagon View Post
With a good shut off valve there shold be no dripping at all. Recommend disconnecting the fuel line at the carb and placing the end in an empty bottle for a period of time. If any gas collects in the bottle it would indicate the shut off valve is not completely effective. A very slow leak in shut off valves (even new ones) is not that unusual. My valve was leaking about two oz. overnight - just enough to allow the carb to leak and leave fumes in the garage. A new valve from Bratton's fixed my problem.
The previous fuel shut-off valve leaked pretty bad -- probably a drop a minute. I did install a new valve, but I understand that even new ones can leak. To check, I opened the drain on the bottom of the cast iron sediment bowl and there was a little gas dripping, but only few drops a day. Eventually it seemed to quit, so not sure if its leaking or just running all the last bit of gas out of the line.


Quote:
Originally Posted by doa44green View Post
My '31 wicks up the inner carb bowl wall and runs out at the gasket surface. I have not found anyone to help me solve this so I just live with it. I installed a ball type shut off valve at the tank. It does not leak!
I thought mine was doing that too. But with a fresh dry gasket, it seemed to stay dry while the wetness initially crept out of the drain hole. Then the gasket gets wet too.

I haven't given up yet, but for now a coffee can gets placed on the engine pan as soon as the engine is off, so while I have gasoline smell in the garage, at least the fluid is contained. After 3 days (temps in 50s-70s), there is about a teaspoon in the can.

What valve did you install? Was it a direct dimensional fit?


Quote:
Originally Posted by mhsprecher View Post
The height of the jets can contribute, if they are too short, i.e. below the fuel level. If the jets do not have a concave surface, they can also leak via capillary action. I had one that was that way and I drilled it a bit to provide a concave rather than convex surface.
The jets came from a generic rebuild kit. Pretty sure they are concave at the tip. I'll have to check when I pull the carb off next time.


Quote:
Originally Posted by RonC View Post
It’s safe practice to turn the gas valve off after use but the carb should not leak if you leave it on. Your float valve seams to be leaking. Use a good original steel valve. Your problem is probably the valve gaskets are junk and leaking. How many are you using?
I am using a viton tip valve. Who sells a good original steel valve? Are they in the rebuild kits?

I have three gaskets -- two red fiber gaskets that came with the valve plus a fiber shim out of a valve shim kit to give me the 5/8" level. To check for gasket and/or valve leaks, I don't have a vacuum pump set-up like some here do, but I did blow with my mouth into the inlet with light finger pressure on the valve. This is not a definitive test, I know, but at first I could hear and see bubbles where the air was leaking out past the gaskets. Made valve tighter and the bubbles stopped. With light figure pressure the valve itself seemed to seal.


Quote:
Originally Posted by 30 Closed Cab PU View Post
Here is previous string https://www.fordbarn.com/forum/showt...lb+fuel+filter
If you do a search - tons more strings on this common subject.

Here is a good site about carbs https://www.modela.org/index.html

If replacing the shutoff valve install a pencil filter in it, trash/rust/grit in the gas tank can quickly ruin a shut off valve since the trash will gouge the shutoff valve inner workings.

Carb shim washers - do not use plastic shim washers or use plastic washers under the jets, plastic does not seal well, use fiber washers.

Jets - if replacing use flow tested jets, Renner's Corner is a good source.
Yes, it is very poor form to jump into a forum without first searching for relevant previous threads. Thanks for reminding me about that specific thread as well as the site. I did read it and many others before diving into my carb. And thanks for your advice here!

Fuel shut-off valve: yes, put the pencil filter in. As an aside, there wasn't one on the previous valve, and I found lots of rust in the settling bulb.

Needle valve shim washers: I have three in there now. The two red fiber washers that came with the valve plus a fiber shim out of a valve shim kit to give me the 5/8" level.

Flow tested Jets: I will consider them.



Quote:
Originally Posted by Ed in Maine View Post
A leaking carb is a real pain. ....... I have found that usually two gaskets are required under the float valve to get a level a bit lower or 11/16 in. to 3/4 in. .......
As above, I already have two plus a shim. Worried that more just introduce more leakage points.


Quote:
Originally Posted by rocket1 View Post
I have tried the viton tipped needle and seat with no success,took it apart and checked for debris shimmed it up and down carb still leaked.I installed original type needle and seat no leaks.
Are the original type needle valves the ones that come with the typical carb rebuild kits?


Quote:
Originally Posted by Fred K OR View Post
Buy another used carb on line and rebuild it. May sole the problem and give you experience in the rebuild process. Buy new parts to put in for the rebuild.
Good idea! This is probably another next step for me. Or maybe $$$ to order a new one!


Thanks,

Doug

Last edited by dougar; 10-12-2020 at 10:05 AM.
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Old 10-12-2020, 10:37 AM   #17
30 Closed Cab PU
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Default Re: Zenith Carb Leak Puzzle

Quote:
Originally Posted by dougar View Post
Thanks, all, for the advice and commiseration. I've quoted a few of your responses below for comments and followup questions.




I haven't given up yet, but for now a coffee can gets placed on the engine pan as soon as the engine is off, so while I have gasoline smell in the garage, at least the fluid is contained. After 3 days (temps in 50s-70s), there is about a teaspoon in the can.


Thanks,

Doug

As an FYI, a plastic gallon milk jug cut in half fits nicely in on top of the engine pan, keeps gas off the engine pan if you need to protect the paint on the engine pan.. Leave the hood open to remind you to remove it before starting the motor.
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Old 10-12-2020, 12:35 PM   #18
Brentwood Bob
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Default Re: Zenith Carb Leak Puzzle

Seems like you have zeroed in on the gaskets for the needle valve.
Multiple gaskets are problematic, also the mating surface in the casting.
Rust from the tank also was mentioned, probably even the Viton valve would have trouble with rust.
Try one thing at a time to get to the cause.
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Old 10-12-2020, 10:04 PM   #19
TerryH
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Default Re: Zenith Carb Leak Puzzle

I bought a properly re-built and road tested carb years ago from Chris Pelikan in Colorado, and it has always worked perfectly. Never leaks, whether I turn the fuel shut off or not....sometimes I forget. It appears that Bert’s is providing the same service now....I highly recommend it!
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