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Old 02-25-2014, 12:00 PM   #1
rfincher
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Default Gas leak from Zenith carb vent hole

I have a major leak at the air vent. When I take the carb apart - no apparent warp, good gasket. I can stop the flow of gas with the float valve with pressure from my finger. Float appears to be at correct 5/8" height.

Can't see the innerworkings of the float valve. Are the float valves originally equipped with a rubber tip to easily seal? My float valve "sounds" all metal.
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Old 02-25-2014, 12:11 PM   #2
jm29henry
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Default Re: Gas leak from Zenith carb vent hole

did the problem happen all of a sudden
or is it a carb you got from some ware ? check the float valve and seat fuel shut off .
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Old 02-25-2014, 12:15 PM   #3
ryanheacox
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Default Re: Gas leak from Zenith carb vent hole

I had a pretty major carb leak over the summer. Turned out my problem was that the float valve had worked itself loose ever so slightly, I tightened it up and now it doesn't leak a drop (of gas). It might not be your problem but it's a quick and easy fix if it is. I'm pretty sure the original valves were not rubber tipped, there are aftermarket ones that do have a rubber coated seat.
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Old 02-25-2014, 12:20 PM   #4
jkeesey
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Default Re: Gas leak from Zenith carb vent hole

The Viton tipped valves work better than standard depending on the manufacturer. Is the float valve you are using standard brass or a replacement? You "should" be able to get it apart to look.
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Old 02-25-2014, 01:07 PM   #5
rfincher
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Default Re: Gas leak from Zenith carb vent hole

I'm guessing mine is not a viton tip since it sounds all metal. Is there a best vendor for that kind of valve?

This is a resurrection project - '29 model A truck that hasn't run in 8 years. Fires up and runs now, I just can't get the carb to hold gas.
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Old 02-25-2014, 01:10 PM   #6
Purdy Swoft
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Default Re: Gas leak from Zenith carb vent hole

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If you are talking about the vent hole on the left or engine side of the carburetor, the problem will be with the float valve or a hole in the float. It can be float level, gasket under float valve, loose float valve, trash in float valve or a faulty float. Yes there are aftermarket viton tipped needles. With real gas viton tipped needles are very good. Ethanol adultrated fuel swells rubber parts and causes the viton tipped needle to stick closed. I've replaced several for that reason. If you are referring to a drip at the small hole under and in front of the choke, the problem could be too short jets under the venturi or too many gaskets under the main jet. any problem that causes the level of the fuel to rise above the level of the jets under the venturi will cause a leak.
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Old 02-25-2014, 01:36 PM   #7
Joe K
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Default Re: Gas leak from Zenith carb vent hole

You can check the float by boiling water and then plunging the float under the surface.

The temperature heats the air within the float and the air comes out the leak and shows as a line of bubbles.

Careful you don't burn yourself.

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Old 02-25-2014, 01:45 PM   #8
jm29henry
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Default Re: Gas leak from Zenith carb vent hole

I don't know but great question
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Old 02-25-2014, 05:26 PM   #9
Tom Wesenberg
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Default Re: Gas leak from Zenith carb vent hole

About 5 years ago I had a speck of dirt get caught in the needle and seat, ao I turned off the gas valve and kept driving. As soon as the engine started to die I turned the gas back on. The inrush of fuel flushed out the dirt and it was fine the rest of the day.
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Old 02-26-2014, 07:26 AM   #10
solidirish
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Default Re: Gas leak from Zenith carb vent hole

What happened to lead you to think that a speck of dirt was on the valve needle? Did this happen while you were driving? Thanks in advance.
Ray in Illinois
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Old 02-26-2014, 10:28 AM   #11
Tom Wesenberg
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Default Re: Gas leak from Zenith carb vent hole

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Originally Posted by solidirish View Post
What happened to lead you to think that a speck of dirt was on the valve needle? Did this happen while you were driving? Thanks in advance.
Ray in Illinois
Yes, I was driving to the store and it started to flood a few blocks from the store, so I just turned off the gas until it started to die, then turned it back on, and the dirt got flushed out.

Back in the 80's I was driving my diesel Rabbit and it started to miss on one cylinder. I figured a speck of dirt must be in the injector, so I figured the easiest thing to try to get it out would be to put a full load on the engine. There was a hill just ahead, so I drove slow to the hill then floored it all the way up the hill. At the top of the hill the engine was running fine again. This sure beat having to remove the injector and taking it apart.
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Old 02-26-2014, 10:39 AM   #12
Mike V. Florida
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Default Re: Gas leak from Zenith carb vent hole

Quote:
Originally Posted by Purdy Swoft View Post
If you are talking about the vent hole on the left or engine side of the carburetor, the problem will be with the float valve or a hole in the float. It can be float level, gasket under float valve, loose float valve, trash in float valve or a faulty float..
Like Purdy says it has to one of those problems as this is the vent for the bowl and the only way for fuel to leak out there is if the bowl is over full from one of the reasons above.
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Old 02-26-2014, 12:00 PM   #13
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Default Re: Gas leak from Zenith carb vent hole

Mine did the same (leaked through the drain) turned out that the needle valve was sticking open because the float was too wide for the housing and got jammed in the housing. A little careful bending fixed it.
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Old 02-26-2014, 12:51 PM   #14
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Default Re: Gas leak from Zenith carb vent hole

I'll stick with a burnished and properly seated steel pin/brass seat valve. Fine rust particles cannot imbed as with softer polymer needle seats. Both Tom W and I have posted in the past about fixing original style steel pin valves. They reliably seal drip-tight and do not stick or glue themselves to the seat if left for extended time.

I don't like the grosse-jet type either. On rare occasion they can get their balls in a knot. When they do work (99.9+% of the time) their steel-to-brass seat is as drip tight as a steel pin valve and they do not suffer rust particle embedment like polymer tip valves.

Viton as a bag of worms. A DuPont trademark, they define 8 grade categories, with multiple formulations in each. Only two, grades "F" and "GFLT" are rated for low fuel permeation (swell resistance) and use with alcohol blend fuels. Many 'Viton' valves fail because they are made with cheaper, wrong, or knock-off fluoroelastomer blends from other manufacturers. If it is an OEM needle from a current (alcohol blend fuel era) carburetor manufacturer the right stuff is used. ANY other aftermarket supplied 'Viton' needle is a crap-shoot.
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