try replacing the fuel filter, the orgional brass ones were known to clog up often. they would let enough gas through at low speed but not enough when you floored it. it is definitely a carb problem or vacuum problem. float too low , leak in float letting gas in float , the bogging would be caused by air and gas not getting into the cylinder at the same time at the correct ratio to burn. a vacuum leak would slow the air flow and a bad carb (accelerator pump) would slow the delivery of thr fuel

I would also agree with the fuel filter, then look into the tank, check to see if you can see alot of dirt and debrise on the bottom of the tank, could be the inlet screen on the fuel outlet of the tank, also know as the sock. Good Luck.

Dave
Mr69vett