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Old 10-12-2020, 09:54 AM   #16
Junior Member
Join Date: Sep 2020
Location: NE Ohio
Posts: 2
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.

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".

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.

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.

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?

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.

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.

Originally Posted by 30 Closed Cab PU View Post
Here is previous string
If you do a search - tons more strings on this common subject.

Here is a good site about carbs

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.

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.

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?

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!



Last edited by dougar; 10-12-2020 at 10:05 AM.
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