The leather is far superior to any of the artifical materials for an accelerator pump.
Having said that, even a leather pump will NOT pump fuel if there is no fuel in the bowl. Modern fuel tends to evaporate from the bowl through the bowl vent (my 390 will evaporate both carbs in less than 2 hours in the Missouri summer!).
To determine if the pump is/is not the problem try the following:
(A) Start the engine. Now you KNOW there is fuel in the bowl.
(B) Stop the engine.
(C) Remove the air cleaner
(D) Open the choke butterfly
(E) Work the throttle from closed to open, you should see a squirt of fuel enter the venturi area. If not, something amiss in the pump circuit (pump, check valve, clogged passage, etc.).
I gave in years ago, and installed an electric pump to fill the carburetor bowls prior to starting.
Jon.
