Zenith float-level guage

[Mad Mac]

I am making a guage to get the correct float level in my Zenith1 carby. Richard Tompkins’ video shows a hose coming out of the drain-plug hole below the cap jet, but I am confused by that: If the main jet overflows due to wrong float level, the fuel would surely just drain out of the choke aperture instead of gravitating down into the drain-plug hose. Or am I missing something?

[Y-Blockhead]

The tube will show you the exact level in the float bowl as seen in the picture on my Marvel. Works the same on your Zenith.

[Jim/GA]

No, you are correct. If you have set the float level that high (very high), it will run out the tips of the main jets. You will get an indication of the fuel level in your gauge, and it will show that it is too high.

Usually you set the float level "dry" (one inch from float seam to the machined gasket surface on the upper carb body). This will get it quite close, not so high as to overflow the main jets (if everything else inside is right).

Then you measure the fuel level "wet" with the clear tube connected to the carb drain plug to confirm the liquid level is 5/8" to 11/16" down from the machined gasket surface of the lower carb body.

Fine tune fuel level by adding or removing gaskets under the float valve body to lower or raise the fuel level. Some parts vendors sell thin gaskets, which helps. I have also rubbed a gasket over some fine sandpaper on a piece of flat glass to make it thinner, when needed.

If your carb leaks out the main jets after you set the dry float level, you need to check:

1. Is the float valve really sealing and turning the fuel flow off? I have seen little brass bits left over from machining in the valve seat that prevent the needle from seating properly.

2. Confirm you do not have an extra gasket installed on the main jet where you screwed it in. Sometimes an old gasket remains behind in the carb body. You don't see it and you install a second gasket on the jet. Now the tip of the jet is too low in the carb body and the correct fuel level will still flow out the tip.

Hope this helps.

[Mad Mac]

Thanks for your replies but I already know those things. My question related only to the drain plug - why connect the plastic gage hose to the drain plug, when any fuel leaking out the tips of the main and/or cap jets will simply drain out past the butterfly?

[Jim/GA]

Originally Posted by Mad Mac

Thanks for your replies but I already know those things. My question related only to the drain plug - why connect the plastic gage hose to the drain plug, when any fuel leaking out the tips of the main and/or cap jets will simply drain out past the butterfly?

Because if the fuel level is correct, it will be below the tips of those 2 jets. So it won't run out the jets to drain past the choke butterfly. The clear tubing open end is also higher than the tips of the jets, so all the fuel will sit at the same level in the bowl, in the jets and in the tubing.

See illustration by Bib Bidonde. He shows the drain plug below the main jet that you are connecting the clear tubing to.

[Mad Mac]

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Thanks Jim, that gives me something to think about.

[Mad Mac]

I'm still confused! Looking through the drain-plug hole with the plug removed, it appears to be blocked by the main jet. Surely that must block any fuel flow and prevent the guage from working?

[jeepguy1948]

If you look at the threads that the drain plug goes into you will see a small hole (an 1/8” or so). That hole goes into the float bowl. That’s how the fuel gets to the jet.

[CA Victoria]

I gleaned this idea from one of the Zenith Carb gurus.
It simplifies setting the float saving time by doing it off of the car. The shim gasket set I use has two thickness .015 & .030. I measured the desired float level (.625 + gasket thickness) and scribed a mark on the plastic bowl.
The apparatus out of the photo is a 1 gallon fuel tank on a test stand about 24” above the carb and a valve inline on the tubing.
........this may not be worth the time to set up if you are only doing one carb......

[Mad Mac]

Originally Posted by jeepguy1948

If you look at the threads that the drain plug goes into you will see a small hole (an 1/8” or so). That hole goes into the float bowl. That’s how the fuel gets to the jet.

Thanks Jeep Guy! That's the answer I was looking for. Don't know how I missed that very small hole. What a great resource this forum is!