My Hyperpak '62 Signet has a problem losing fuel pressure after driving and getting the engine hot. It isn't a fuel pump problem, as we have tried two high pressure electric pumps with the same results. The car is losing pressure from 6 to 8 lbs cold, to 2 3/4 lbs immediatley after running, but in an hour or two it builds back up 6 to 8 lbs when I restart it. The same when running high performance runs. We have run with a full tank; run without the gas cap; run without the fuel pressure regulator installed, and used both a Holley blue and another brand high output (120 gallons per hour) electric pump. I wonder if the fuel sock inside the tank is stopped up, or kinked, or something, but that doesn't explain everything. With the car running at idle, at about 3lbs pressure, a persn can take off the gas cap, cup his hands and blow hard into the gas filler opening and the force of this air adds about 3/4 lb of pressure on the fuel regulator. Just removing the cap at idle has no effect, without blowing hard into the filler tube. What can be causing this? All the company experts we've called at Holley and Edlebrock are baffled. My mechanic has tried everything they've recommended. And yes, the pump IS lower than the tank. The fuel line is 3/8" and seems to be large enough. Can you suggest a possible cause/cure? Thanks.

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Restored '62 Signet, 229 4bl, Offy intake, auto, Dual Dutra exhausts, shaved head and block, high stall converter, 1.6 roller rockers, etc.