The Ford Barn

fiftychev · 02-01-2016, 03:09 PM

I have a Marvel carb and it is leaking out of the GAV entry. I have rebuilt the shut off and it does not leak. But the carb leaks some. Is the GAV supposed to seal when totally closed or do I have the float set wrong. Any advice is appreciated.

Tom Wesenberg · 02-01-2016, 03:19 PM

Could be the float is too high, or the casting might have a crack at the GAV threads.

Tom Endy · 02-01-2016, 03:34 PM

The GAV boss should be a pipe thread so as to seal off. I use a small amount of pipe dope on the threads. Quite often someone in the past may have run a regular tap through it which will destroy the sealing capability.

Tom Endy

fiftychev · 02-01-2016, 04:17 PM

It appears that the leak is not at the threads but where the shaft exits the brass fitting.

fiftychev · 02-01-2016, 04:19 PM

Is there a procedure for checking the float position and adjusting if necessary?

duke36 · 02-01-2016, 06:25 PM

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Had the same problem. The gav needle is supposed to have a rubber ( nitrile ) or leather washer on the step portion below the spring, but interestingly enough, one of my other Marvels, the needle has no step. Using very little teflon pipe sealant on the housing threads and a fibre washer above the threads also seemed to help with the leak. Also tried different float needles and the one with a viton tip worked the best. The available double ball float valves wouldn't seem to seal well but not sure why.The float should be parallel (horizontal) with the casting mating line as noted in other threads. Some like adding more fibre washers under the valve, but I bend the float tab very slightly.

02-01-2016, 03:09 PM	#1
fiftychev Junior Member Join Date: Oct 2012 Posts: 23	Marvel Carb Leak I have a Marvel carb and it is leaking out of the GAV entry. I have rebuilt the shut off and it does not leak. But the carb leaks some. Is the GAV supposed to seal when totally closed or do I have the float set wrong. Any advice is appreciated.

02-01-2016, 03:19 PM	#2
Tom Wesenberg Senior Member Join Date: May 2010 Location: Mpls, MN Posts: 27,582	Re: Marvel Carb Leak Could be the float is too high, or the casting might have a crack at the GAV threads.

02-01-2016, 03:34 PM	#3
Tom Endy Senior Member Join Date: May 2010 Location: Southern California Posts: 3,168	Re: Marvel Carb Leak The GAV boss should be a pipe thread so as to seal off. I use a small amount of pipe dope on the threads. Quite often someone in the past may have run a regular tap through it which will destroy the sealing capability. Tom Endy

02-01-2016, 04:17 PM	#4
fiftychev Junior Member Join Date: Oct 2012 Posts: 23	Re: Marvel Carb Leak It appears that the leak is not at the threads but where the shaft exits the brass fitting.

02-01-2016, 04:19 PM	#5
fiftychev Junior Member Join Date: Oct 2012 Posts: 23	Re: Marvel Carb Leak Is there a procedure for checking the float position and adjusting if necessary?

02-01-2016, 06:25 PM	#6
duke36 Senior Member Join Date: Jun 2015 Posts: 1,425	Re: Marvel Carb Leak Sponsored Links (Register now to hide all advertisements) Had the same problem. The gav needle is supposed to have a rubber ( nitrile ) or leather washer on the step portion below the spring, but interestingly enough, one of my other Marvels, the needle has no step. Using very little teflon pipe sealant on the housing threads and a fibre washer above the threads also seemed to help with the leak. Also tried different float needles and the one with a viton tip worked the best. The available double ball float valves wouldn't seem to seal well but not sure why.The float should be parallel (horizontal) with the casting mating line as noted in other threads. Some like adding more fibre washers under the valve, but I bend the float tab very slightly.