Since you say it starts fine first thing in the morning but not after sitting for a few hours and you see black smoke coming from the exhaust while trying to start it, I'm guessing that some of the fuel injectors are worn out and leaking fuel into the cylinders after you shut it off and causing the engine to be "flooded", i.e. the fuel to air mixture has too much fuel which cannot ignite.

You can do a simple check to see if this is a possibility, when you are having this issue and it's not wanting to start, after the initial attempt turn off the ignition and go and get close to the exhaust pipe and see if it smells of raw gasoline, if so this maybe the problem.