MG Car Repair: MG Midget stall-out, vacuum gauge, manifold vacuum

Question
I have a 1979 MG Midget,I have rebuilt it and added the aftermarket weber carb and intake. Recently the car will idle and run for about 1/2 mile then stalls out. It will start again and then do the same. I have checked fuel filter and lines. The gage shows 3lb of gas. But when it stalls it dropes down to 1lb. Can a machanicle pump be intermitten? Should I change out to an electric pump?
I also had the catalatyc converter burn up on me. The shuo said the car is probably running rich. Should I take it off?

Answer
Hi Nathan,
That depends on if the pump pressure drops to 1 PSI then the engine stalls shortly afterward or does it drop to 1 PSI after it stalls?
Even at 1 PSI the engine should keep running as that means there is still fuel pressure to the carb and the carb has enough fuel in the float chamber to run a short time after a pump goes to zero pressure.

If you know a CAT is burned up you should test for exhaust back pressure as that can shut an engine down. A rough test can be done with a vacuum gauge on the intake manifold. Set the idle at a fast idle and read manifold vacuum. Don't change the idle speed and watch vacuum. If you see manifold vacuum decrease as the engine runs and the vacuum continues to drop until the engine dies then that is a strong indication the CAT is stopped up (which can happen when they burn up)

A 100% test is to either remove the CAT and do a test run or drill and place a small piece of pipe in the exhaust before the CAT and read the pressure on a gauge. (most vacuum gauges have a low pressure scale for testing fuel pressure) I found that most British cars that I tested can't handle any more back pressure than 1.5 PSI (even at full throttle)

Excess fuel going into the exhaust for any reason will melt a CAT.
Howard