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Old 10-09-2020, 08:42 AM   #1
Junior Member
Join Date: Sep 2020
Location: NE Ohio
Posts: 2
Default Zenith Carb Leak Puzzle

Iím a Model A newbie and have just joined this forum; apparently with my new-to-me 1931 Coupe, Iíve also joined the leaking carburetor club. Iíve been doing a lot of reading in this forum and recommended files online, but I am stumped. Sorry this post is so long.

BOTTOM LINE UP FRONT: Biggest problem is that gas seems to be coming out of the fuel bowl vent and/or the idle jet & compensator well vent on the engine block side of the carb. With a small mirror and bright light, I can see the wetness running down that side of the lower casting. Eventually a few drops per day come off the body bolt.

BACKGROUND: I bought Les Andrews' book, replaced the supply line & fittings, installed a new fuel shut-off valve under the tank with pencil screen filter, cleaned/rebuilt the cast-iron sediment bowl on the firewall, and rebuilt the carb. In the carb:
(a) I took a brand-new Viton-type float valve apart and cleaned off any obvious burrs on the internal edges of the brass housing and needle.
(b) Float itself was checked (no bubbles in hot water, correct weight, hinge is not bent).
(c) I believe the main and cap jets are the right height, although initially there was dampness in the air inlet. I believe this was due to the main jet and/or cap jet gaskets leaking so I tightened them, twice.
(d) I used a float-level visualization kit to be sure the fuel level is 5/8" below the upper gasket surface. When I first reassembled the carb, the level slowly rose and then gas came out of the vents at a fairly high rate Ė like a drop a minute. I found out that the new gaskets on the float needle valve were not sealing. Re-tightened, and the level held.

PUZZLE #1: I left the float-level visualization kit in place for a day or two. The level clearly held at 5/8", but after a while, gas was weeping out of one or both of the vents, resulting in a couple drips a day. As a test, I re-installed the drain plug, drove the car, turned off the fuel shut-off valve, and just let the engine die. No "leak" wetness below the vents initially overnight, but eventually it was obvious the next day. Is it possible for gas to creep up the wall inside the bowl or up the idle & compensator cavity and come out the vents?

PUZZLE #2: After sitting for several days, gas began dripping (although slowly) from the air inlet drain hole, too. That stopped, but thereís still dampness in the inlet. And of course the couple drops a day originating from the fuel bowl vent and/or the idle jet & compensator well vent continues. Am I back to square one?

Thanks in advance for your time and thoughts.

Doug Rohn
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