To Start the engine, I need to push the gas pedal to the floor (WOT) then crank. (Note: I do NOT "pump" the gas pedal, just push all the way to the floor.)

Starter spins quite a while, then the engine roars to life.

This is particularly true if the engine is warm/hot, but even when Cold (at least this summer) this is required.

Initial timing is 8 BTDC, Vacuum-Advance, Holley 4bbl.

What likely is the cause?