Ya got a point there Jerry, she’s all stock 1950, and I got’um full fuel tank also, which puts tops out about level with the air cleaner. Back to the drawing board. I’ll give the pump a test and see if the check valve is solid. Not sure if the symptom fits though, she runs right along at highway speed.
Then again, it might just be time to put that new double action pump on that I’ve been saving for a rainy day. Just didn’t want to get into the vacuum plumbing quite yet.

Jerry is right as far as Vapor Lock taking place on the vacuum side. In an airplane this becomes a real problem the higher you go when using standard auto fuels. Avgas is formulated with a higher vapor pressure because of the decrease in pressure at altitude. As the pressure on a liquid decreases it wants to convert to a gas. Just the opposite is true, that’s why liquids with a very low vapor pressure like liquid Nitrogen or Oxygen are stored under pressure, at standard pressure they are a gas.
Thanks guys for your thoughts.
I’m swinging more along the lines of there maybe is something has gone wrong in the good old Rochester ‘B’ or else as Jerry suggests, the pump is going getting ready to go south.
Then again maybe the check valve had some crud wedged under it. Now that I think about it, when I cleaned the fuel pump sediment bowl out there was this one strange piece of thin silver plastic or paint flake about 1/4"x 3/8" all by itself in with the rust powder. I didn't think much about it because I was thinking, that's what the screen is in there for. But if that got stuck in the check valve that could cause the problem that Jerry described. An inline filter before the pump might also be on the addenda for this weekend.
Denny Graham
Sandwich, IL

Denny G
Sandwich, IL