When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Dirty fuel tank, dirt in the carb, not enough movement to the pump arm. Pull the line to the carb, run the line to a separate container and see how much fuel your pump is putting out. (CAUTION, HAVE FIRE BOTTLE ON HAND AND DO THIS OUTSIDE)
Also could be the plugs are fouled and fail to fire under heavy load. How long since a tune up, points, plugs, timing, etc?
This can also be caused by a coil that's heading south but not quite done for yet, or a bad condenser/points. Many "carb problems" are ignition problems. Check for proper vacuum advance operation too.
Check the resistor on the firewall. I was having same issue and thought it was vapor lock but when the resistor heated up truck would act like it wasnt getting fuel. Replaced resistor after fuel pump,carb rebuild and viola.
I would also suggest checking the vacuum advance for a leak. If that is OK make sure that the distributor breaker plate moves when vacuum is applied. If it isn't moving and you can find someone with an old Sun distributor machine attached are the specs at various RPMs. This chart says late '50 and all '51 but I think it applies to '52 also. Maybe someone else on FTE can verify that.
Then of course you should check the vacuum while the engine is running. Attached is a handy chart which should help.