Zenith carb leak solved FINALLY

[TJMack]

Like many others I've been plagued with a leaking Zenith carb that has been driving me crazy trying to fix. I looked back at the numerous threads on this subject, even my own from 2017 when I had the same problem with another car. Like almost everyone else I figured it had to be the needle and seat valve. Well, it wasn't. I won't bore you with all the ass-ache I went through to get to the point where I have finally stopped the leak

In some of the threads I saw mention of a "dimple" on the float that could affect the needle valve. I checked my float but couldn't see any "dimple" so I discounted that as a possibility. That was my mistake.

After reaching my tolerance level of frustration I figured there had to be something that was preventing the needle valve from closing entirely. The only other part in the mix is the float.

With my reading glasses on, and the float held just so in the light, I could see a mark where the needle touches the float. I wouldn't call it a dimple, it was so small and insignificant. But I figured I had noting to lose by polishing it out.

Using 400 grit wet-or-dry paper I polished the surface to be as sooth as possible. I reassembled the carb and let it sit. I have a sight gauge on the carb so I can tell the fuel level. This time the level stayed where it was suppose to be. It has been over 24 hours and still good. Before, it would rise to the point of leaking within two hours.

The next time I run into this I'm going to polish the surface even higher, probably to 800 or 1000 grit. If you think about it, the needle has to skid along the surface of the float as it closes. The amount of movement is so small it wouldn't take much to interfere with smooth operation, especially considering what little pressure is exerted by the action of floating the float.

It's hard to believe how something so insignificant can cause such frustration. I hope this helps someone else avoid it.

[Gary WA]

Good job and a good outcome! Simple things do work.Thanks for the update for others to see your results!

[Gene F]

So this was on the float tab, or that cross brace of the float? Been a while since I had one apart...

[nkaminar]

TJ, Thank you for the report. It is so important for Barn members to report fixes that work so that we all can learn.

[gdmn852]

Hello, I believe he is talking about the float tab . I have wondered about lapping the needle and seat would help also, get a better and more precise fitting of shutout area angle.

[Bob C]

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Marco (RIP) mentioned this on his web site.
https://web.archive.org/web/20141105...hop/carb-1.htm

[BButturff]

This has been plaguing me also. Thank you.

[TJMack]

Originally Posted by BButturff

This has been plaguing me also. Thank you.

That picture shows the dimple very well. On mine it was just a very slight mark in the same spot, but enough to cause trouble. I wonder how many others are having the same problem and don't realize it?

[BButturff]

Originally Posted by TJMack

That picture shows the dimple very well. On mine it was just a very slight mark in the same spot, but enough to cause trouble. I wonder how many others are having the same problem and don't realize it?

I'd bet many. Like you, I've read several posts and watched many videos to try and figure it out. I've replaced the float valve 3 times and also replaced the float. I've used the sight gauge and even intentionally set the float level low but the fuel level still creeps up after about an hour. I'm one of those guys that hates leaks so it's been driving me absolutely NUTS! Thanks again for sharing what you learned.

[TJMack]

BButturff, You did exactly what I went through so I'm sure you know the same frustration. Please let us know if the fix works for you as well.

[henry's 31]

Hi TJ:


Thank you so much! This is why I love this Forum. When you share items like this it helps so many of us keep our beloved "A"'s on the road. THANK YOU ALL!

[TJMack]

ADDENDUM: Polishing the float arm fixed the sticking needle valve problem but there remained a very slight drip from the throat of the carburetor when it sat overnight. Placing a new paper towel on the splash pan under the carb showed it quite nicely. I could tell the float level was good by my home-made float level gauge so it was really bugging me. I figured it had to be something else letting a minute amount of gas into the throat of the carb.

Sure enough. When I took the carb apart again to check the main and cap jets I found that the main jet was just a little bit loose. I tightened it up this morning and so far no dripping. We'll see how it looks in the morning.

[BButturff]

Polishing the float did the trick for me, no more gas leaks so now I can focus my OCD on something else such as my leaking shocks!

[JoeCB]

TJM , thank you for posting... it is often said , "nothing succeeds like success"

Joe B

[jack wingard]

Everyone that fixed the carb leak now needs to fix their leaky gas shut off leak also. That is if the carb leaked with the valve in the off position.