If you have added headers there is likely a heat problem with one of the primaries coming too close to the starter without heat shielding. If you do not have headers then the stock heat shield may be missing if it is a heat problem. You could also have a tired starter that is heat challenged. I have used paint thinner cans cut into sheets to wrap around exhaust pipes that come close to the starter to provide rust free heat shielding. I tie them to the exhaust with monel wire or stainless .063 tig wire. These are the most common heat problems involving the starter. If you have too high a timing setting, then the engine will roll over much harder when hot and cause a nearly no crank condition. A flooded engine will hydraulic if too much fuel is in the cylinder at restart if for instance the power valve is blown and filling the engine after shutdown. Leaking injectors can contribute to hard cranking if you do not have a carb. Do any of these causes fit your problem?
Bruce