Gabriel - much as I enjoy throwing rocks at the Rochester B's ( wink ); the carburetor probably is not the issue here. Rather it is the volatility of modern fuel. The Rochester B can leak down, but only if you park the truck on its roof (upside down wink ) Leaking down is a function of Holley carburetors, with the diaphragm type power valves, and a gravity passage direct to the intake.

Jon.

Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify.
If you truly believe "one size fits all," try walking a mile in your spouse's shoes!
The Carburetor Shop