Here's the test procedure we used for a lot of years:
1. Disconnect the gas line at the carburetor, and plumb it into a catch container of some sort. The most common one was a 1-qt. oil can, back when they were round, and made of metal. Start the engine and idle. The pump should flow a minimum of 1 pint in 30 seconds. The gas in the carburetor float bowl should be plenty for a 30-second idle time without stalling.
2. Attach a pressure gauge to the fuel line. Run the engine. The pressure should rise to a steady 3-5 lbs. and stay there for a short time after the engine is stopped. (10 seconds or more)
3. Attach a vacuum gauge to the inlet side of the pump. Run the engine. The vacuum should go to 12-15 inches of mercury, and stay there for a few seconds after shutdown. The above tests check out the inlet and output check valves. Replace the pump if it fails either of the check valve tests.
4. If the pump is low on volume, but passes the check valve tests, look for a restriction or an air leak on the input side. Attach the vacuum gauge to every fuel line connection from the pump to the tank- - - -at the flex line, and every line connection all the way back to the tank outlet. If it holds vacuum at the tank outlet line, the problem is inside the tank. I once found a 2-inch long grasshopper lodged in the tank pickup line on my first car, a 47 Mercury convertible. That car would run 1 mile and starve out, repeatedly.
Jerry
