Ok, now it's starting to sound like a fuel starvation problem. Have you checked you fuel filter and fuel pump? I had a very similar problem and found (2) fuel filters installed. One was under the hood which I found right away. That other was back by the fuel tank under the bed on the passenger side. That one looked to be completely clogged. I removed the new one under the hood and moved it back to the OEM location, replacing the old one. The filter needs to be installed before the fuel pump. Not after.

Also, check to make sure your timing is set to 0? with both vacuum advance tubes off.

Last, check you plugs to make sure they're tight in the head. If they're loose in the head they'll misfire from poor grounding.

Ok, one other thought berfore I go. You could also have a bad Accelerator Pump. If the carb is leaking down at night it will crank right off the bat in the morning but then run like crap when it runs out of the initial fuel load. That's why I really think you have a fuel flow problem. But it could be a combination of things as well.