Holley NH Carb Seep Problem

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Model T Ford Forum: Forum 2015: Holley NH Carb Seep Problem
Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 15, 2015 - 09:10 am:

A friend has a problem with a Holley NH Carb seeping gas out the air inlet.

The carb has been rebuilt with a new float and needle valve and appears to work OK other than that problem.

The real mystery is how gas can flow up hill to leak out the back.

The first theory was that an intake valve was not seating properly and blowing some of the fuel mixture out the air inlet.

A valve job did not appear to help the problem or change the compression numbers.

Are there any other suggestions that might help?


Top of pagePrevious messageNext messageBottom of page Link to this message  By R.V. Anderson on Thursday, January 15, 2015 - 09:29 am:

Check the bowl vent; make sure it's clear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kenny Edmondson, Indianapolis on Thursday, January 15, 2015 - 09:41 am:

The seat for the needle valve doesn't seal well to the body of the carb on any of the replacements needle and seats. The gaskets are too hard. I air check all of my seat installations. I end up making my own gaskets.

To air check, use a rubber tipped blow gun. I put air tool oil between the seat and carb body, then hold the needle in the seat with my finger and then shoot air into the inlet. You'll see lots of bubbles come up between the seat and carb body.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve Jelf, Parkerfield KS on Thursday, January 15, 2015 - 09:48 am:

Some carbs have "slept with the fishes" and the body under the seat is too rough to seal even with a good gasket. You may need to smooth that surface before installing the gasket and seat.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Thursday, January 15, 2015 - 10:04 am:

WHEN is the gas leaking? All the time or just when choking?


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 15, 2015 - 10:14 am:

All the time, but only a very slight occasional drop actually drips.

The air intake area does appear damp and stay wet.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, January 15, 2015 - 10:22 am:

R. V., the bowl vent was plugged and that kept the carb running over rather heavily.

That was also a problem on a carb last year and the first suspect of this problem.

This one was plugged solid.

Basically, the air bubble did not let the gas level go high enough to allow the float to cut off the fuel supply.

The carb casting is rust free and it has never been soaked in the sea either.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Thursday, January 15, 2015 - 10:41 am:

Might just be some crud from the gas tank. Take the fuel inlet elbow off and check. Even a small speck of rust will not allow the needle to fully close filling the bowl up and will drip. If there is crud in the inlet flush it and the bowl out. Allow some gas to flow through the fuel line and drain off the sediment bowl from the gas tank then check what comes out. Also might want to check the float setting.


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