Hot starting problems are usually fuel related. When a hot engine is shut off, the temperature of the engine and everything on it continues to rise for awhile as the engine undergoes a period of "heat soak." This can cause fuel to boil inside the carburetor bowl, fuel lines and fuel filter. When you attempt to restart the engine, "vapor lock" obstructs the flow of fuel and the engine doesn't want to start.
This is much less of a problem on fuel injected engines because the fuel is usually under much higher pressure inside the injectors and fuel line. Even so, a fuel line routed near an exhaust manifold or a fuel rail that's exposed to a lot of heat may still suffer the same kind of problems.
Heat soak problems such as these can sometimes be cured by wrapping insulation around affected fuel lines, and/or installing an insulating spacer or heat shield under the carburetor.
Hard hard starting tends to be a seasonal problem, but may be worse in the early months of spring when refiners are switching fuel blends. Gasoline refiners produce fuel with a slightly lower volatility rating (called "Reed vapor pressure") during hot summer months because lower volatility fuel is less likely to boil and cause hot starting problems. During the winter, they switch to a higher volatility fuel because it makes cold starting easier. But if you still have "winter" grade fuel in your tank when warm spring weather arrives, you may experience some hot starting problems. The problem will go away, however, as soon as the refiners in your area switch to their summer grade fuel.
Hot starting problems can also be caused by cooling problems that allow your engine to run too hot (the pistons swell up and may scuff the cylinder walls), or excessive resistance in the starter motor that causes the engine to crank slowly. A starter "amp draw" test can be used to check the condition of your starter. Also, many starters have small "heat shields" to protect them from heat radiating from nearby exhaust pipes or manifolds. If the shield is missing, the starter may get too hot and bind up.