Not an expert but....
Since the starter is laboring when you try to do a hot restart, I'd guess that your engine is loading up with fuel (rich).
This can be caused by either too much fuel supplied, a weak ignition, or an engine that is slap worn out (which kind of "tricks" the carburetor with low vacuum).
IMO too much fuel is usually a choke staying closed, a poorly adjusted idle mixture, novice carburetor modifications, a ridiculously dirty carburetor, or the carb overflowing with fuel.
Ignition problems depend on the ignition in place, quality of the components, and/or age of the components.
Once these types of issues start loading the engine up with fuel, the plugs get dirty, which in turn makes the problems even worse and round and round.....so the plugs usually need changing or cleaning.