RUNNING RICH, REASON ?

I'm just going to go out on a limb and say it just todays worthless gas!
If it's just a summer cruiser and sets all winter.....Well that oxygenated fuel Is no Friend, setting in the fuel bowl all winter long.
Can of carb spray to the outside and maybe even, pulled apart to do the same on the inside.

If it has backfired, Investigating the Power Valve, is a vary good idea. Blow/bad power valve will make it rich at idle but not at full throttle.
You said it had black smoke out the back when you throttle it......crap in the needle and seat cause the fuel bowl to be too high.
causing carb to run rich...............
I could be way off but that's were my mind goes.