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

Mike,

I'm certainly not an expert, but since nobody else is answering you, I thought i'd offer a couple of suggestions. What the carburator guy told you may be right, but I would be a little skeptical. Check the float level to make sure it is not above the level of the jet. You also do not mention what your fuel pump type, if any is. If you have put an electric fuel pump that is of positive displacement type ,it may be trying to hold pressure to the carburator causing a little gas to seep out when its stopped.

Mike - don't think we were the ones who did your carb, but the information you have posted is certainly true. To explain further:

With an updraft carb, fuel is pulled UP into the engine by vacuum. So there is a certain amount of fuel in the upper throttle body, and the intake manifold at all times when the engine is running. When the engine is turned off, the vacuum disappears, and gravity takes over for any fuel in suspension at that time.

If you look at the design of your BB-1, you will see that the engineers took this into account, as the air intake is turned slightly upward to provide a "holding puddle" in the bottom of the carburetor.

As the BB-1 had some marine applications, and leaks are unacceptable in marine applications (leaks are followed closely by booms), Carter provided a "boss" in the center of the low area in the air intake which has a small orifice and the boss is tapped with an 1/8 inch pipe thread. Most Carters have an unused vacuum tap (capped with a plug) above the throttle plate. On marine applications, a copper tube with a "drip loop" was connected from the low tapped boss to the vacuum port. The drip loop would catch all of the fuel preventing leaks. The next time the engine was started, engine vacuum would pull the fuel from the tube into the engine, enhancing the choke function. Many other of the better updraft carburetors (Stromberg, Zenith, etc.) incorporated the same feature.

Modern fuel can add to the problem, as volatility can cause pressure in the fuel line after the engine is shut off, dumping additional fuel into the carburetor which can fall out through the main discharge nozzle. Again, the design of the BB-1 will minimize any actual leak.

If you do have a leak, you could always incorporate the marine "drip tube" into your system. If I have insufficiently explained, feel free to call during normal business hours, and I will be happy to further explain.

Jon.