BB1 CARB HELP

[mikzjr@aol.com]

I HAVE A 29 CHRYSLER WITH A BBI CARBURATOR, I SENT IT OUT HAD IT REBUILT AND WHEN YOU TURN THE CAR OFF GAS COMES OUT THE OVERFLOW TUBE ON THE BOTTOM OF THE CARB, ALSO GAS RUNS DOWN THE LINKAGE THIS PROBLEM ONLY HAPPENS WHEN YOU TURN THE CAR OFF A LITTLE GAS RUNS OUT THEN STOPS. THE GUY THAT REBUILT IT SAID THAT IS WHAT UP DRAFTS DO IT IS THE UNBURNT GAS IN THE MANIFOLD FALLING DOWN IS THIS TRUE. MIKE

[oldford]

I'm not a carburetor expert, but my first guess is that the float is set too high. Try lowering a bit, say 1/8". And no, updrafts don't leak by design...

Frank

[Mark Shaw]

Could be true. I have seen others comment on this problem.

I have the same carb on my 13 Buick and I always shut off the gas when parked. The metal seated needle valve will leak due to rattling in the seat for so many years. Unless your rebuilder changed the needle & seat, you will have a leaker. The float just doesn't push hard enough to seal drop tight. You might try using some fine valve grinding compound to mate the needle and seat for a better seal.

Harold Sharon (no longer with us) used to modify needle valves with a Viton cone tip to provide positive shut off. I don't know of anyone doing this now.

[mikzjr@aol.com]

IT'S NOT THE FLOAT, THE LINKAGE THAT HAS GAS RUNNING DOWN IT IS TOWARDS THE TOP OF THE CARB THE FLOAT IS AT THE BOTTOM AND IT ONLY LEAKS DOWN THE LINKAGE WHEN THE CAR IS FIRST SHUT OFF AND THEN THE LEAK STOPS.

[oldford]

That indicates raw gas above the venturi at the throttle plate. My guess is that the gas travels back down the throat and passes out through a worn shaft or bushing. Are you running an electric pump that has too much pressure? It could be a bunch of things that need to be eliminated one at a time. Clearly there is too much gas (and I'm not being a wise guy here...)

Frank

[mikzjr@aol.com]

NO ELECTRIC PUMP IT IS A VACUMM TANK.

[carbking]

Don't know who did your carb, but he/she is basically giving you the correct information.

With an updraft carburetor, fuel is pulled up from the carburetor into the intake manifold and then into the cylinder head by engine vacuum. When the engine is turned off, vacuum goes to zero. Gravity will cause all fuel suspended in the intake manifold, and possibly part in the runners of the cylinder head to drop.

If the carburetor throttle is improperly adjusted (too rich) and the throttle plate is completely closed, then the fuel will gather on the throttle plate, and exit the carburetor around the area where the throttle shaft extends through the throttle body.

Alternately, if the carburetor throttle is properly adjusted, and cracked slightly open, then most of the fuel will fall completely into the air intake of the carburetor.

Many carburetors have a drain from the air intake and just drain this fuel (usually an amount less than a tablespoon) onto whatever is below the carburetor.

Marine carburetors in particular (and others) did not permit this draining due to the possibility of an explosion in a closed bilge (also why they use bilge blowers). Marine carburetors would have a closed tube that ran from the drain on the air inlet to a vacuum source ABOVE the throttle plate. The gas previously in suspension would fall into the air intake, where it would drain into the tube and stay until the engine was started. The vacuum of the engine would draw the fuel into the intake system and aid with the initial mixture for starting.

Jon.

[mikzjr@aol.com]

JON THANKS FOR THE INPUT, I RAN IT AGAIN TONIGHT AND AFTER I SHUT IT OFF I ADVANCED THE THROTTLE ON THE COLUM AND NO GAS RUNNING DOWN THE LINKAGE, AND LESS THEN A TABLESPOON ON THE GROUND. BY LOOKING AT THE THROTTLE PLATE CAN'T SEE ANYWHERE TO ADJUST IT OTHER THEN THE IDLE SCREW. IT IDLES GREAT AND RUNS GREAT. ANY SUGGESTION.

[carbking]

Check my profile for home page where you will find telephone number. Give me a call during normal business hours, and will be happy to discuss with you.

Jon.