Gas leaking from carb after shut off

carol ann

carol ann

Member
Hi all, I have a 1931 model a with a zenith 2 carb (with the side mount fuel filter on the carb). The car starts right up and runs great but after i turn it off and close the fuel shut off valve to the carb. the gas leaks out of the carb. Since the car runs so well i did not want to start messing with the carb until i checked with the experts. It is not the drain plug and the gas shut off valve works. Thinking it may be the float but i would suspect that the car would not run so well if it was the float. I would appreciate any ideas - this is my first model a and i don't want to drive it around until i solve this. thank you
 
First I would try closing the fuel shutoff valve Before you shut the engine off, and let it run the gas out of the carb bowl, until it dies on it's own....

If in the morning there is still gas leaking from the carb maybe your fuel shutoff valve is leaking just a little...just enough!
 
Ok, i will try that....what stumps me, and i am not a mechanic by any definition, the car runs so well ....so in my layperson's thinking, is the gas leaking when it runs??? in other words if I run it is there a safety concern ...or is this occurring after the car is shut off. are there any suggestions on how to figure that part out. thank you
 
Your gas shutoff valve is not holding if you have gas leaking. I had the same issue until I changed my valve.
 
carol ann said:
Ok, i will try that....what stumps me, and i am not a mechanic by any definition, the car runs so well ....so in my layperson's thinking, is the gas leaking when it runs??? in other words if I run it is there a safety concern ...or is this occurring after the car is shut off. are there any suggestions on how to figure that part out. thank you
Click to expand...

After a short drive open the passenger side hood and look at the carburetor. If it is wet it may need gaskets or maybe the inlet/fuel pipe is seeping a little...

If it is dry it could be just the heat expansion of the fuel after you park...

Does it leak from the sides, bottom, or the air intake? Does it have an air filter?
 
You say that car runs Ok and the shut off valve works Ok so i would suspect that from the following list your problem is minor leak from one or more of items 9-13 in the following list. Do the easy thing first- dry the carb, turn the gas on and see if you can see any external seepage - often the inlet union threads are the source but leaks always drip from the lowest part of the carb,
Here's the hit list for Zeniths:Causes of leaking.
( and PS some very poor quality and leaky float valves come in some of the kits)
Problem: Remedy
1 Leaking/loose float valve gasket: Tighten/reseal/replace
2 Leaking float valve: Replace
3 Friction on float hinge: Loosen
4 Incorrectly set fuel level: Re-set
5 Hole in float: Repair or replace
6 Cap jet or Main jet too short/ more than one gaskets on main jet: check
7 Leaking/loose gasket at main jet: Tighten/reseal/ replace
8 Leaking /loose gasket at cap jet: Tighten/replace
9 Leaking or loose GAV housing threads: Tighten/ reseal/ replace
10 Leak at fuel inlet union: Tighten/reseal/replace
11 Loose/leaking gasket at strainer: Tighten/reseal/replace
12 Loose/leaking gasket at drain plug: Tighten/reseal/replace
13 Cracked housing/leaking passage plugs: Repair or replace
1-8 will generally manifest as poor running,
9-13 will generally not affect running unless xs leaking
 
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thank you everyone - this is all very helpful; it is so great to have this model a community! now i have my homework to do and I will report back.
 
I don't understand how you could have a leak if the shutoff valve is working properly. Mine was leaking at the sediment bowl, which was the result of 2 issues. The valve leaking and the sediment bowl gasket needed to be replaced.
 
I think 1955cj5 may have a good way to check it out. I have the same problem and I tried to see if gas was leaking just after I turned off the engine. In my case, I found there was no gas on the bottom of carb after a run. But I still have not found the problem. Am still working on it.
 
I "thought" Minervas' valve was OK, BUT, after runnin' all the gas out of the carb, after sittin' 2 days, she would start, WITHOUT turnin' the GES ON!
Solved with a $4.99, hardware store pet **** type valve, that fit PERFECTLY, in place of the original.
 
Fred K-OR said:
I think 1955cj5 may have a good way to check it out. I have the same problem and I tried to see if gas was leaking just after I turned off the engine. In my case, I found there was no gas on the bottom of carb after a run. But I still have not found the problem. Am still working on it.
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Another thing to try would be after it sits for awhile, run you finger a little ways down from where the strainer screws in. If gas there, then this fitting is leaking. Also try the same a little ways down from the gas inlet, if gas there then that fitting is leaking. If neither of these have wet gas under them and there is gas on the bottom of the carb, then it would have to be maybe the bottom drain plug or the gasket between the two parts. I suppose there could be other things, but here are a couple of other things to check. Guess like mentioned it could also be a crack somewhere.
 
I just had to change out the shutoff valve on my '31 PU that I recently purchased-it would leak a pint or two of gas overnight through the carb-a terrible fire hazard. Turns out the tapered part of the valve had a groove worn in it, and it would never seal-only a valve replacement cured it.
 
you've all been so helpful so i went out to check several of the recommendations. I was able to take a video of the leak happening...but i need your help in knowing what this means. The car is cold and has not been run in a week. there is about a cup of gas that has collected in the container i placed under the carb. there is still a drip from underneath but it only happens about every 30 seconds. I towel dried the entire carb surface and took a mirror and flashlight to check to check and make sure all surfaces were dry. everything was dry. then with the camera rolling on the mirror under the carb, i opened the gas shut off valve for about 2 seconds to fill the fuel line to the carb then i closed the shut off and began filming. the video is of the underneath of the carb, the nut you see on the left is the drain nut. the area to the right is just under the choke valve with the air opening to the right (off video). there is a tiny hole that starts out dry and then shows the gas dripping. I am hoping this is familiar to someone who can tell me what they think needs to be fixed. i am not very familiar with carbs but i can follow directions and i look forward to getting feedback.
 
To find the origin of a slight leak, use the corner of a BLUE paper towel. Be sure to check the float bowl vent hole, behind the BACK of the carb, where the lower & upper carb joins.
modelabasics.com shows this very clearly & also LOTS of GREAT info & has some really GREAT ANIMATED INFO!
Bill W.
 
Carol Ann,
I'll bet that your gas valve isn't shutting off completely, that design valve is common for that. PLEASE consider the Hardware Store pet **** type valve, they NEVER FAIL. Only $4.99 & fit perfectly in place of the original valve, take an old valve with you for a SAMPLE.
I hope the Purists will forgive me, BUT, who wants their car to BURN or have a smelly garage. ALSO, snug up ANYTHING on the carb, that might SEEP GAS.
When I got Minerva, I was prepared to overhaul the carb, as she seeped EVERYWHERE. While waiting for the carb kit, I tightened everything on the carb & PROBLEM SOLVED! While the valve is off, install the stainless, "pencil" filter in the top of the valve, they're a GODSEND!
Bill W.
 
hi Bill, thank you for the model a basics website - it looks great.
i hear what you are saying about the gas valve shut off and i will replace it. there is one thing i am not getting: is it normal for gas to drip out of that small hole under the choke valve on the bottom of the carb? I do have a video but can't seem to upload it to this thread.
 
carol ann said:
hi Bill, thank you for the model a basics website - it looks great.
i hear what you are saying about the gas valve shut off and i will replace it. there is one thing i am not getting: is it normal for gas to drip out of that small hole under the choke valve on the bottom of the carb? I do have a video but can't seem to upload it to this thread.
Click to expand...
That hole is a "SAFETY" DRAIN, so gas doesn't puddle up & go BOOM! They ALWAYS drip after CHOKING, or if anything is leaking internally in the carb.
Bill W.
 
Carol look at the top of the cap jet in the pictures, it is very close to the level of gas normally in the float bowl. If the float is set a little to high and the level of gas is a little higher than top of jet gas will leak out the jet until level drops. This type leak will always happen after shut down but then stop after a bit. Shutting off fuel from under dash will prevent this simply by starving the float of fuel to leak. You should be able to park a car with no gas leak with fuel valve wide open. Reset float lower. Old guys would do this without even taking carb off car, one bolt bottom comes off everything you need right there. Good Luck
 
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