Congrats on purchasing a great boat and welcome to Team Talk.
For starters, your engine is a 351 Windsor.
To remedy what sounds like a rich situation, I would hit the basics first:
Check spark plugs...might be pretty black by now.
Do you still have points.......if so confirm correct dwell - don't rely on point gap
Confirm choke opening fully by 90 seconds
Turn mixture screw in until lightly seated and count number. Should be close to 1 1/2 turns
Confirm base timing at 10 degrees or whatever spec says
Clean flame arrestor.
With all that done, I suspect that you have too rich a power valve in your carb. Should be 2.5 though some carb numbers spec a power valve closer to 5.0
Tandem Axle Wheel & Tire Package $659
4 S5 or S5 Black 14x5.5 wheels, 4 ST205/75R14 Kenda Loadstar tires
Single Axle Wheel & Tire Package $399
2 S5 or S5 Black 14x5.5 wheels, 2 ST215/75R14 Kenda Loadstar tires
MOUNT, BALANCE & FREE SHIPPING INCLUDED IN BOTH PACKAGES
CARB REBUILDING - FAST TURN-AROUND - $100 +PARTS
LED lights, Hubs, Spare Tire Carriers, Chrome & Powder Coated Lug Nuts - Red, Blue & Black
PM or email me firstname.lastname@example.org