Leaking float valve

M

Mad Mac

Senior Member
Hi from NZ,
The ball-type float valve in my Zenith carby leaks badly and I don’t know why. I have done all the things recommended on this forum and in numerous videos but it still leaks. The float is correctly positioned 5/8” in relation to the casting, the Main Jet and Cap Jet apertures are correctly positioned in the venturi 3/8” below the casting, and the float valve even cuts off properly when I blow through it, while holding the float shut.

I am sure the leak is in the float valve (and not elsewhere) because the fuel level in the sight glass guage rises right up to the top of the bowl and fuel starts coming out through the gasket.

My next move will be to check if the float leaks by submerging it in hot water, but I don’t think that is the problem. Anyone got any suggestions?
 
If you have the float 5/8” from the bottom of the casting when turned upside down then your float level is way too high. The float seam should be approximately parallel to the casting. If that is set correctly and the float closes when you manually hold it then either there’s a leak in the float or the hinge pin is sticking for some reason.
 
Sometimes it's not the float valve at all but the ability of the float valve gasket to seal against the upper carburetor casting. Remove the valve and gasket and check the surface that the gasket seats against. It could be scored or badly pitted. Try using nylon gaskets instead of fiber gaskets and don't be afraid to lean a bit hard in your tightening of the float valve. Good Luck.
 
Especially check the float bowl gasket sealing surface if you’ve bead blasted the upper housing. If that surface is pitted then the gasket won’t seal and you will leak as you describe. Been there, done that.

I think the 5/8” number is the fuel level vs. the casting with the valve closed. My recollection is that the seam is about 1” from the casting when turned upside down, but yes, parallel to the casting.
 
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Thodge said:
If you have the float 5/8” from the bottom of the casting when turned upside down then your float level is way too high. The float seam should be approximately parallel to the casting. If that is set correctly and the float closes when you manually hold it then either there’s a leak in the float or the hinge pin is sticking for some reason.
Click to expand...

Thanks. Yes the float seam is parallel to the casting. When I install the clear plastic tube as a float-level guage, the fuel rises way above the correct level in the bowl (so high that it reaches the gasket between the 2 halves of the carb). That surely proves that the problem is a leaking float-valve because if it was not leaking the fuel would never get that high. Is my logic correct?
 
bobbader said:
Sometimes it's not the float valve at all but the ability of the float valve gasket to seal against the upper carburetor casting. Remove the valve and gasket and check the surface that the gasket seats against. It could be scored or badly pitted. Try using nylon gaskets instead of fiber gaskets and don't be afraid to lean a bit hard in your tightening of the float valve. Good Luck.
Click to expand...

Thanks, I will check that. Also, I will try to obtain some nylon or rubber O-rings that are fuel-resistant.
 
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Did someone mention the "dimple" problem in the float arm where it contacts the valve needle? If there is a worn in "dimple" it can catch on the needle and keep it from closing. ( maybe that isn't an issue with the ball type valve?)

Joe B

correct fuel level is below the bowl gasket surface, condition of that sealing surface and gasket should not be an issue. (assuming car is on a level surface)

Re-reading all this, it appears that you have the float level way too high. The fuel level as set with the clear tubing method is to be 5/8 " below the bowl gasket joint. Either bend the float arm and/or add gaskets under the float valve to adjust the fuel level.
 
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JoeCB said:
Did someone mention the "dimple" problem in the float arm where it contacts the valve needle? If there is a worn in "dimple" it can catch on the needle and keep it from closing. ( maybe that isn't an issue with the ball type valve?)

Joe B
Re-reading all this, it appears that you have the float level way too high. The fuel level as set with the clear tubing method is to be 5/8 " below the bowl gasket joint. Either bend the float arm and/or add gaskets under the float valve to adjust the fuel level.
Click to expand...

Thanks Joe,
There is no dimple, just a very slight depression and I can't see the valve sticking on that. I am certain that my float is set at the correct level, based on numerous you-tube videos on that subject. If it is not the float level, it must be a poor seal at the float valve, although I can see no pitting in the valve seat. This is so frustrating!
 
This afternoon I put a brand new float valve in and added another fiber washer to get the float seam parallel with the casting surface, as it was before. I also immersed the float in hot water to look for air bubbles and there were none. So the float is not leaking.
 
That is strange. Maybe try removing the float bowl and holding a glass jar in its place so you can check the movement of the float. Or with the bowl removed hold the float closed and see if it stops the fuel flow. I’m wondering if there’s a crack in the upper housing.
 
This is getting frustrating, even for us observers..... What I would do at this point...
Shut off the fuel at the tank - drain the carb - install the clear plastic fuel level tube - turn the gas back on and observe the fuel level as it rises.
If the float is set correctly, you should see the fuel level rise quickly to the 5/8 " level below the bowl joint. Then if there is a leak the level will rise slowly until you see leakage.
If the initial "quick" fill goes above the 5/8 line, the float is not set correctly, or you have a very serious leak somewhere.
Joe B
 
Another thing is the carb half gasket built many carbs one is wider than the other and the float hits the gasket either cut down or get the right width one?!Just another idea to look at.
 

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Recently I put a Model A Zenith carburetor back on my pickup for Touring Class judging. I went through the carburetor before mounting and set the float level as outlined in Gordon Biggar's book "Restoring the Model "A" and "B" carburetors the "Rex" Reheis Way". He recommends setting the float 3/16" to 1/4" lower then the published setting of 1 3/32". I have attached his procedure below.
 

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JoeCB said:
This is getting frustrating, even for us observers..... What I would do at this point...
Shut off the fuel at the tank - drain the carb - install the clear plastic fuel level tube - turn the gas back on and observe the fuel level as it rises.
If the float is set correctly, you should see the fuel level rise quickly to the 5/8 " level below the bowl joint. Then if there is a leak the level will rise slowly until you see leakage.
If the initial "quick" fill goes above the 5/8 line, the float is not set correctly, or you have a very serious leak somewhere.
Joe B
Click to expand...

Thanks again Joe,
The first time I did that, the fuel in the sight-glass rose quickly to the 5/8 level and then half an hour later it had climbed slowly up the tube to the casting surface. That indicated a correct float-level and a slowly leaking valve.

Then yesterday after I put a new float-valve in, the fuel in the sight glass rose immediately to the casting surface, indicating a quick leak and possibly that the float level is not set correctly.

I will check the float level again, as I have done many times already.
 
Check the vent hole in the float chamber.It is vented to the atmosphere,and if a bug gets in there it will hold the float open.As the gas runs it in the air has to exit,and if it can't the valve can stay open.I had heard of it,but until it happened to me I truly didn't believe it could happen.It happened to me on a reman carb that had set on the shelf for a year.I went round looking for cracks,split gaskets,wrong height jets,wrong tipped jets,defective valve,when I remembered somebody telling me about the vent hole possibility.I found a bug in it,blocking it off.With all the careful time put in that carb I had a really drip free carb after that.It was OK while driving,but about 20 seconds after shutting it off it would start to leak,heavily.
 
Mad Mac, lots of god advice for you above but be warned- you may have been right first time! When I was rebuilding carbs and selling parts a while back I came across several brand new float valves (of all types and from several suppliers) that did not work properly. So much so that I stopped selling them unless I had personally tested each one individually.
 
I bet it is not the float. bet it is that one jet dos not have the little dimple in the end.
 
Thanks Guys - some great advice there:
I respond as follows:
Gene F: Both the Cap Jet and the Main jet do have a dimple at the aperture.
Keith True: The vent hole in the float chamber is clear - its not blocked
Fullraceflathead: Thanks, I will check for cracks in the threaded area
Al in NY: Thanks for your very good material. I will read it carefully.
John Buckley: The float is not new - was used in this carby before and worked OK.
 
Hi again: I have discovered the problem at last: The brand new float-valve was leaking. The leak stopped as soon as I replaced it with the old one. Not sure what was wrong with the new one, which I bought from a reputable Model A parts supplier.
 
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