Fuel seeping from GAV

Thodge

Thodge

Senior Member
I have a strange problem with fuel seeping out the top of the GAV housing when the car sits overnight. Two mornings in a row I’ve gone in the garage to a fuel smell and small spot of fuel under the car despite shutting off fuel and running out of gas the night before. So it would seem that the valve has a slow leak and needs replacing. But how could the fuel level possibly be high enough to come out the top of the brass GAV tube? At first I thought it was just loose in the carb body so I tightened it only to have it do it again this morning. It was also wet above the level of the threads, indicating that it is definitely coming out the top of the tube. I tried closing the GAV against the seat when I parked it today so we’ll see if that makes any difference. Has anyone had this happen? Could it be heat related?
 
gravity..........the old aqueducts of Greece could propel water 36' high through gravity.


might want to try Permatex or similar.
 
The only way gravity can come into play is if the float valve is open. The float would be hanging open after running the car out of gas and should close once the fuel shutoff lets enough fuel back in to fill the bowl. So far the only theory I can come up with is that the fuel shutoff has an extremely slow leak that causes the float bowl to fill so slowly that the float hangs up a little. That would let the fuel level get over the top of the jets and the GAV tube before it finally closed. If it starts up tomorrow morning with the shutoff closed, then I’ll at least know for sure I need to replace the valve.
 
I’ll be watching this closely. I had a similar problem last fall and I never found the cause. I honed the shutoff valve and checked the float valve and all was good. I finally gave up and bought a new carb. No more leaks. I hope you can just fix yours.
 
Just posting an update on this issue. Sure enough, the car started and ran for 30 seconds after it had been run out of gas and left to sit a while. So I plan on replacing the tank shutoff as soon as I’ve burned some of the fuel in the tank. Then I can move on to the potential float problem. Wouldn’t surprise me if the new float valve is leaking because everything else in the rebuilt kit I got was junk so that probably is as well.
 
Hello, Glad you found problem and posted what it was .My experience hasn’t been altogether favorable either, replaced the quarter panel and door on my 31 roadster, the repro moldings on door and panel didn’t align with each other.A lot of rework to get them to fit up properly.
 
As a side note to the last 2 posts I've found EVERY repop part I've purchased needs some type of work to make it look right or fit right or even work.
 
Isn’t it amazing with all of the advancements in technology that we still can’t even copy a 100 year old design and make it work as well as the original?:)
 
Thodge said:
Just posting an update on this issue. Sure enough, the car started and ran for 30 seconds after it had been run out of gas and left to sit a while. So I plan on replacing the tank shutoff as soon as I’ve burned some of the fuel in the tank.
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Ensure you get the new style shut off valve with the ball valve inside. Much better that the old valve. Also you will need the new style pencil filter, the old pencil filters do not fit the new valves.

https://www.snydersantiqueauto.com/product.htm?pid=979339&cat=41707

https://www.snydersantiqueauto.com/product.htm?pid=1076974&cat=41707
 
That’s exactly the valve and filter I”ll be using. Out of curiousity, does anyone know how much fuel is left behind in the tank with the raised pickup level of adding the pencil filter? I’m fairly certain mine doesn’t have one right now, based on the amount of sediment I get in the bowl. Just wondering if it makes a significant difference in the amount of reserve fuel after the gauge hits empty. Not that I plan on running it that low, just nice to know.
 
Isn’t it amazing with all of the advancements in technology that we still can’t even copy a 100 year old design and make it work as well as the original?

of course it can be done- its called money.
 
ronn said:
Isn’t it amazing with all of the advancements in technology that we still can’t even copy a 100 year old design and make it work as well as the original?

of course it can be done- its called money.
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How much more could it cost to copy and make a part that is correct that already exists?
 
[QUOTE=Y-Blockhead. How much more could it cost to copy and make a part that is correct that already exists?


My feelings, exactly. After all, these cars were designed and manufactured to an affordable price point originally, yet they were NOT junk. It should still be possible.
 
Am I missing something? has anybody answered this conundrum?
Thodge said:
.... how could the fuel level possibly be high enough to come out the top of the brass GAV tube? ...It was also wet above the level of the threads, indicating that it is definitely coming out the top of the tube. /QUOTE] The only way I can understand fuel coming out of the top of the brass GAV is A) bowl air vent blocked as well as both comp and main jets blocked or B) a brass GAV housing that is shorter than spec.
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How much more could it cost to copy and make a part that is correct that already exists?

apparently, a lot.

None of the fenders that are copies fit for starters.......... The amp meters are all junk today......the list goes on and on.
 
johnbuckley said:
Am I missing something? has anybody answered this conundrum?
Thodge said:
.... how could the fuel level possibly be high enough to come out the top of the brass GAV tube? ...It was also wet above the level of the threads, indicating that it is definitely coming out the top of the tube. /QUOTE] The only way I can understand fuel coming out of the top of the brass GAV is A) bowl air vent blocked as well as both comp and main jets blocked or B) a brass GAV housing that is shorter than spec.
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It seems that the top of the GAV tube on this carb must be just slightly lower than the level of the jets. When I removed the choke rod and driver from around it, the fuel was definitely coming out there. This is on a good running car with a newly cleaned and rebuilt carburetor so blockages aren’t the culprit. It has to be the new float valve acting up.
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The saga continues with this leaky Zenith. Dropped the float bowl today to put the old float valve back in, assuming that the repro was leaking and causing the fuel level to overflow the jets. I found that it wasn’t overflowing at all and if anything the fuel level was too low. Despite this, there was still fuel seeping from the GAV tube and was also wet in the throat of the carb around the jets. But how? The fuel was well below the top of the jets. Checked that the jets were tight and they were so the leak isn’t there. Logically, the only way fuel can go uphill is if there’s pressure behind it or suction in front of it. I’m thinking maybe a blocked bowl vent. I only found one orifice that looked like it could be the bowl vent and blew compressed air through it to make sure it was clear then put it back together with the old float valve. The car is running well but time will tell if it still leaks. Are all of the bowl vents the same on these? I thought I read somewhere that the early carbs (this is a late ‘28 Zenith 1)had smaller vents or am I imagining that? The photos show the fuel level in the bowl as I found it after sitting for a day and the fuel on the outside of the carb body. Any thoughts?
 

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Thodge said:
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The car is running well but time will tell if it still leaks. Are all of the bowl vents the same on these? I thought I read somewhere that the early carbs (this is a late ‘28 Zenith 1)had smaller vents or am I imagining that? The photos show the fuel level in the bowl as I found it after sitting for a day and the fuel on the outside of the carb body. Any thoughts?
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The fuel level that you are looking at in the bowl, separated from the top half of the carb, does not have the float sitting in it, so it is much lower than the actual fuel level when all is assembled.

If you want to see the actual fuel level in the carb when it is assembled, use one of those clear plastic tubes that connects to the bottom plug of the carb. Put it on the car and turn the fuel on. Watch the level in the tube.

Then you can turn the fuel valve off and monitor the fuel level in the carb as it sits. If it rises up more overnight, the fuel valve or float valve (or both) are leaking.

Don't worry about the bowl vent size changes over the years, that is not what's causing this.

You might need a very light coat of a non-hardening thread sealer (not teflon tape) on the GAV piece that screws into the carb body. You might have gas weeping out those threads. I use Permatex #2.
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