I had a similar problem that was caused by the MC plunger not coming out far enough to expose a pressure relief opening. I backed my plunger out 1/6 of a turn and the problem was solved. I was amazed that only 1/6 of a turn could make that difference.


1948 3/4-Ton 5-Window Flatbed Chevrolet

34 Years. Now with a '61 261, 848 head, Rochester Monojet carb, SM420 4-speed, 4.10 rear, dual reservoir MC, Bendix up front, 235/85R16 tires, 12-volt w/alternator, electric wipers and a modern radio in the glove box.