Classic/Antique Car Repair: 56 chevy sputtering when hot, holy moly, bad vibes

Question
Hey Brad, appreciate your help. I have a '56 chevy pickup with a 235 straight six. Old Muddy has been a good runner for over ten years. I had to park it in the garage for a while due to surgery (on me) but right before I did, it started acting like a "chug - a -bug" when it was hot. acting like it ran out of gas. It would stall out and start back up. well I thought maybe I was passing debris from an old tank, so recently upon getting back in the groove to drive it, I put a glass fuel filter in it so I could monitor gas flow. (it also has a glass bowl fuel pump cause I'm into original stuff) drove it, noticed some real rumble thru the tail pipe on downshift, pulled back in the driveway to show my girl what a genius I am and it started "chugging and running rough intermittently" Popped the hood and Holy Moly I see air bubbles in the fuel filter and my fuel pump!!! I don't leak gas, or smell it in the cab, Heck I don't leak anything. If it is an air leak in the line wouldn't it be all the time ? Maybe my girl and her Lexus give it bad vibes ! Hah ! ps: the last time I drove it before my sugery it more than "rumbled" on the down shift it "backfired" well, caused people to "duck" on the sidewalk ! (I have a glass pack about 12 years old) Thanks and God Bless you

Answer
The fuel line has at least one section that is higher than the level of the fuel in the tank. If the line has a rust out pin hole in one of these high areas then that car break the vacuum between the tank and the fuel pump. To check that disconnect the fuel line from the tank at the pump. Attach a vacuum gage to the fuel pump and crank the engine. You should see about 11 inches of vacuum and it should hold for several minutes after you stop cranking. Then reconnect the line and disconnect it at the tank. Attach the gage to the line and crank again. You should see the same vacuum and it should hold for several minutes. If not there is a pin hole in the line. Good luck and hope you are all in one piece after surgery.
Brad