Leaking Zenith Carburetor

[TJMack]

I’m new to Model A’s. The one I have now is the first one I’ve ever owned. But I’m not new to carburetors. I’ve worked on them since the late 50’s when I took apart my family’s first power mower, an 18” Roto Rugg.

Over the many years I’ve also worked on carbs from numerous cars, trucks, a few tractors, outboard motors, chain saws, etc, a Chris Craft inboard, even my airplane. But I have to admit this “simple” Zenith on my Model A has caused me more agony than any other I can remember.

I’ll also admit that I never bothered to learn all the theory of operation and detailed workings of a carburetor. I only needed the basic understanding of what did what, and what to do when it didn’t. This usually amounted to cleaning, or at most changing, the float valve (we always called it the needle-and-seat) and making sure the float actually floated. Along with a good cleaning and new gaskets, and I was usually back in business.

Not so with this Zenith. As it turns out, it should have been, but I spent hours chasing my tail on the damn thing.

My first thought was to clean the float valve and make sure the float wasn’t taking on gas. The float valve is one that doesn’t come apart, so cleaning it was a blind operation. Shaking the float I couldn’t hear any sloshing, and actually trying it in both water and gas verified that it, in fact, did float.

Upon reassembly the leak persisted. It took me quite a while to even figure out where the gas was coming out. To make a long story as short as possible, after more attempts at cleaning the valve, I finally figured out that it was coming out the main jet and the cap jet into the throat of the carb.

Now, anyone who has messed around with these has also figured out that the level of gas in the reservoir is critical. That’s because if it’s too high it will leak out the main jet and the cap jet as mentioned above. I found this by taking the bottom of the carb off and slowly adding gas to the reservoir to it to see where it was coming from into the throat. Nothing happened until the level of gas got almost to the top of the reservoir and then out it came. A quick observation showed that the fuel in the reservoir was now above the level of the main and cap jets. As soon as it got below that level the flow stopped.

This may seem obvious, but until you actually do this check, it’s not at all obvious, and hard to see with the carb assembled. You can’t see the fuel level in the reservoir.

Since we all know that the level of gas in the reservoir is controlled by the float valve and the float, I was back to the original thoughts that one of them must be bad. I ordered a new float valve and a new float even though I couldn’t find anything wrong with the old ones, which at some time had already been changed by a previous owner.

Upon installation of the new parts I was hopeful that the problem was solved. Not so. The new float valve leaked as bad as the old one. The float was obviously a waste of money. So was the float valve.

The interesting part of all this is that I reinstalled the old parts and for now at least, it isn’t leaking. I don’t know if I really learned anything new, but it kept me out of the bars, as my Mother used to say. It did verify that not all that is new is necessarily better.

For some reason I hadn’t even thought to check on-line to see if anyone had similar experiences. This is what led me back to the Ford Barn. I had actually signed up for it last year a couple months after I bought the car, but honestly forgot all about it. Dumb, I know, but like lots of people my age I suffer from CRS.

I have since found an EXCELLENT, well written article written by Tom Endy that would have steered me in the right direction if I had only seen it earlier. I do intend to spend some time on the carb when the car sets idle in Florida for the summer. Thanks to that article I feel confident that I can improve it.

One question I have, though. Does a Model A tend to leak if it’s parked on a hill? It seems as though it must if the car is facing up hill. That could place the level of the jets below the fuel level in the reservoir and allow it to leak out which would lower the float and allow more fuel to flow in. Eventually this could drain the tank, I suppose.

I can see why it’s so important to close the shut-off valve under the tank whenever the car is not running.

[katy]

Did you check and/or adjust the float level to spec? Or slightly under.

[Sparky]

A float level gauge is a handy diagnostic tool to have. It's only a few bucks, and all the Model A suppliers have them.

[Y-Blockhead]

Welcome to The Barn TJ.

Edit: After re-reading your post, the following may not pertain. I thought you were asking about the carb leaking when sitting. Sounds like yours is leaking when running?? I left my incorrect response because it may help someone with the problem I described. Good luck...

I know this sounds off the wall but check the Tank Shut Off Valve for seepage. I have found that if it seeps just a little there is not enough head pressure to keep the float needle valve seated and the carb will dribble out the hole in the bottom of the throat.

With the Tank Shut Off Valve closed try disconnecting the gas line at the carb and put a pan under it to catch any gas. Empty the pan and place it again under the gas line and let it sit overnight. In the morning if it has a little gas in it, the Tank Shut Off Valve is seeping.

I fear this is one of the reasons you see people install a second valve in the gas line.

Good luck.

[TJMack]

Katy, yes, I checked the float level numerous times, and did try setting it lower. Even that didn’t work. I knew what was causing the leak, the float valve not holding, but I couldn’t figure out why. It was driving me crazy.

Yblockhead, it was leaking with the engine off, and I presume it leaked with it running as well. So your idea of the shut off valve being the culprit is an EXCELLENT theory!

During one of my numerous think sessions while staring at the split carb, I actually had a thought that maybe it was related to the head created by the gas in the tank, but my idea was diametrically opposed to yours. I was wondering if, for some reason, the valve was not able to hold the head. I quickly dismissed the idea after thinking of the fuel pressure generated by a working fuel pump.

The reason I especially like your theory is the fact that my shut-off valve was in fact leaking a little. I knew this and had one on order, but they were back-ordered so I was left with time to dream up all sorts of solutions for the leak while I waited for it to come.

I never thought it would solve the float leaking problem but I think you hit the nail squarely on the head. I usually know better than to change two things at the same time when trying to diagnose a problem. I violated that rule on this. The shut-off valve came in the same shipment with the new float valve and float. Not thinking that the shut-off valve might be the root cause, I went ahead and put in the new one, and then installed the new float valve and float before trying it.

As I mentioned earlier, the stupid thing still leaked when I got done, but I unfortunately at this time can’t remember if I tried it with the shut-off valve closed. The frustration level had risen quite a bit.

For the hell of it, I decided to put back the original float and float valve and give it a try. When I did, all was well again. The new float valve must be defective or just have something in it. But you can imagine how that messed with my mind.

So it looks like you deserve one at-a-boy. Your theory is most ingenious and thoughtful, and most likely the answer that I’ve been looking for. I’d like to buy you a beer!

[michael a]

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I thought about it too will you buy me a beer also

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[michael a]

After my silly response I was thinking what a wonderful thread this was. These new aftermarket parts will make you want to crap in your hands and smear it in your hair.

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[Dutie]

Hello T J ,
Y Blockhead was right on the money. I had the same issue with the zenith leaking nanno amounts past the float valve. The firewall valve on my 31 roadster leaked enough to pressure it through the float valve. Put in a new one with the new viton seat and it still leaked. Finally I installed a positive in line shutoff and my issue was over. Been four years now and no issues at all and yes it will leak as you say when you face it uphill and park it. Just remember to shut the in line off and you're all set. Think my in line came from Brattons for about 50.00 Good luck Dutie

[1930 coupe]

I check float valves by blowing on them with my mouth. You should not be able to get any air through the valve with light finger pressure on the needle.
Then I install the valve and float on the housing and turn it upside down and blow in the fuel inlet with my mouth. With just the weight of the float on the needle, you should not be able to get any air through it. If the gasket surface on the housing has rust pits, you might get some leakage between the gasket and the housing. This can be corrected with a small amount of permatex on the gasket.

[Gary WA]

Site Index (Model-A.org)

[Gary WA]

Use the above link for more info , and Thank you to the originator of link.!

[TinCup]

Great write up here. Tom's articles are always on point and early on I relied on them when starting on carbs. Sounds like you are on target and their have been some good suggestions already posted. I will just add that I too like the Viton tipped float valves that have been changed to work with alcohol gas. One thing I have found from time to time is that if the vent on the gas cap is plugged the tank will pressure up and force gas through the main cutoff valve which almost always leak some. Do they all leak? No but a great many do due to faulty setup and parts. Keep at it and let us know the conclusion.

[TJMack]

Addendum: The saga continues. All is not as well as I thought. There’s still a leak. The new tank valve did stop the leak when it is turned off, but not when it’s left on. At least I’m seeing some progress. J

This afternoon I left the tank valve on when I got done with my drive just to verify that the leak stopped. At first there was no leak. I didn’t check it for a few hours, but when I finally did, there it was, the infuriating drip out the throat of the carb.

Tomorrow I’m going to try a few things, one at a time. The first is I’m going to split the carb and then dry the area around the float valve real well by spraying it with brake cleaner and let it evaporate.

Then I’ll hook up the gas line to the upper half and invert it so that the float valve is closed by the weight of the float. I’ll turn on the tank valve then inspect the carb for any indication of where the gas comes out, if it does.

Hopefully this will give me a lead on what needs fixin’. I’ve already looked for cracks in the casting, but they could probably be so small that the eye can’t see them. When I changed the float valve I inspected the casting where the gasket goes and it looked OK, no major pits. So I don’t know what to expect.

If this experiment turns up nothing I’m going to expand on Yblockhead’s theory. I noticed that my fuel line is slightly kinked. Maybe this is reducing the head pressure to where it’s not enough to maintain the fuel level. I KNOW…. It’s a reach but I’m getting desperate.

Another thing, other than Yblockhead’s theory, that makes me suspect of the fuel line is the fact that the see-through fuel filter I have just in front of the carb inlet quite often looks empty even with the engine running fine. It seems that once the float valve opens the filter should fill with gas before the carb reservoir.

To further complicate this mess is the fact that I’ve had trouble with the condenser overheating. That’s another long story for a different thread, but I fixed that with a heat shield that I made and put under the distributor.

The reason that this may be germane to the conversation is that in testing my heat shield I let the car idle for 10 minutes or more after a good warm-up to test the effectiveness of the heat shield.. Before the heat shield I couldn’t get it to run for more than a few minutes if I stopped and let it idle. As it sat there idling I was watching the fuel filter. It always looked empty, but I could see a very faint trickle of gas passing through if I looked real close..

It finally did stop running, but I thought it ran out of gas by the way it stopped. I carefully took out the drain plug in the bottom of the carb and sure enough, nothing came out.

I still haven’t figured this one out but I’m thinking Yblockhead’s theory might be in play.



1930 Coupe, one of the first things I did was the blow test. It suggested that everything was OK. I’d like to have my vacuum tester that I have up in New York down here in Florida. It would be more conclusive I think.


Gary Wa, thank you for that link. That looks very interesting. I'll have to spend some time there;.

[TJMack]

Sparky, I really like that fuel level gauge. I'm going to make one if I can find the right fitting for the drain port. If not I'll buy one the next time I order some parts. thank you for posting.

[1930 coupe]

You will need to drill a hole in a drain plug, then cut the threads off a tubing connector and solder them together to make your fitting.
Also if the cast iron seat area under the jets is pitted, you can get seepage from under the jet gaskets. A little pertamex on the gaskets will fix it.

[johnbuckley]

I have across several brand new float valves that leak, no matter what type... conventional, or ball,or viton tipped... I now test them all before fitting. It is so fustrating to fit a new part and find it's defective.

[redmodelt]

Biggest issue with all most all the needle type seats is you cant take the needle out easily to inspect. If the point is not polished correctly there is no way to get them to seal. I know that was an issue with Model T valves for a while. Sometimes little bit of brass is still in the seat area from machining, if those are not removed, same thing. Other thing you could try is tapping the needle lightly to seat it.
You may or may not know; to adjust the float, you add shims under the needle valve not bend it.
Also, there were some main jets on the market back some time ago that were a little on the short side.
Do you have the gasket installed under the jets?

[TinCup]

Try repeating the test and leave the gas cap off.

[old31]

Originally Posted by michael a

I thought about it too will you buy me a beer also

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Ya, well I thought about it before you, so I get the beer.

[1931 flamingo]

Re-ck the float height.


Paul in CT