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Old 01-23-2013, 06:47 PM   #1
Larry Dowell
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Default leaking carb.

I have replaced the shut off valve and rebuilt the carb but still leaks at carb when it sits over night not sure what to do next.
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Old 01-23-2013, 07:07 PM   #2
1crosscut
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Default Re: leaking carb.

Check to see if the shut off valve is still leaking. Even new ones can leak. You can pull the line off the carb and put a can under it and see if it leaks any overnight.
If that isn't the problem than it's probably gas left in the carb finding its way out after you shut it off. If you don't already shut off the gas and run the carb dry at the end of your drive I would suggest that you do so.
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Old 01-23-2013, 07:54 PM   #3
Tom Endy
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Default Re: leaking carb.

If the shut off valve does not have a positive shut off you then have to rely on the float valve holding. This is not always possible. A little piece of rust from the gas tank can off-set the valve. Best to replace the shut off valve.

If you are going to rely on the float valve you should consider the following:

1. A viton tip float valve works best.

2. The float level has to be set accurately. If the fuel level rises much above the 5\8" set point it will spill over the top of the main jet and the cap jet and fuel will run down into the throat of the carburetor, exit through the small drain hole and run back to the hex nut under the main jet and drip in the floor.

3. If the float has been molested by someone trying to adjust the float level it may not come up straight and it will cock the float valve causing it not to seat properly.

Tom Endy
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Old 01-23-2013, 10:20 PM   #4
larrys40
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Default Re: leaking carb.

Larry,
when it's leaking.. put a finger in the carb throat at the choke shaft, if it's wet inside like Tom said the float level is too high, either because the needle and seat are sticking or it's just too high. If it's not check carefully around the carb bottom to see where the leak is coming from. Drain plug, crack, etc.

Set float to 5/8 I check needle and seats with a vacuum gauge. If it won't hold vacuum they are going to leak. I check them of course out of the carb. I like the viton tips but have sometimes had mixed success. Some of the "Steel" seats need to be slightly staked on the workbench to give a little set. Lightly tap the float end on the workbench to seat it into the seat slightly. My mentor Terry Oberer taught me that a few years back when I was having some chronic seat issues... and by golly... it does do the job at times. Do NOT do this to Vitons.. you will ruin them! Sometimes you just have to switch needle/seats. Again.. the vacuum test tells the most accurate story. As Tom said the floats sometimes get molested and worn. Make sure there is no "dished" out area on the float where the needle touches. If there is, dress it smooth and flat with a dremel... I also like to bench test a carb with a float gauge and fill line actually filling the carb with gas. If you do that and let it sit ( must be same level as on engine in car), you can see what it's going to do on the car. When I install them them I know they should be good.

Lots of guys out there with great knowledge more than me.. that's just some of my experience. Good luck!
Larry Shepard
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Old 01-24-2013, 06:41 AM   #5
western77
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Default Re: leaking carb.

I have had carbs with a crack from the drain plug up the threads to the bowl. Very hard to see but gas keeps dripping out one drop at a time untill the bowl is emty. JB
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Old 01-24-2013, 07:11 AM   #6
Joop
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Default Re: leaking carb.

These sites will help you

Click here: Gas Leaks from Carburetor (Model-A.org)


Click here: Carb Basics Go to Trouble Shooting


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Old 01-24-2013, 09:19 AM   #7
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Default Re: leaking carb.

Mine does the same thing. It will drip onto the splash apron and then to the floor at a slow enough rate to make a 4" ring on the floor as it evaporates. Mine is a leaky shutoff valve. I have a new electric one but need to do some wiring changes before installing it so haven't gotten it done yet.
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Old 01-24-2013, 10:55 AM   #8
Purdy Swoft
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Default Re: leaking carb.

It could be caused by a repro main or cap jet that is too short. I use original numbered jets. It could be caused by too many gaskets-washers under the main jet. Too many gaskets under the main jet lowers the jet below the level of the gas in the float bowl in the carb. If the main jet sits too low it will continue to drip gas. I avoid the viton tipped needle valve because todays fuel can cause the viton tip to stick shut.
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Old 01-24-2013, 12:35 PM   #9
Larry Dowell
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Default Re: leaking carb.

Thanks for all the help will try it all very informative great help
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Old 01-24-2013, 12:48 PM   #10
Brentwood Bob
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Default Re: leaking carb.

At one time the fix for a rusty tank liner was to mix up some permatex and alcohol as a gas tank coating. The alcohol, I believe, attacks this liner, and the fuel has a film that deposits on the float valve. The valve sticks if you leave fuel in the bowl, say from not running the motor after you shut off the gas. Marvel Mystery Oil in the fuel, or some diesel are possible additives. It is a PITA to remove the carb and free up the float valve.
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