Not sure if I am posting this question in the correct section but here goes.
I just acquired a fully restorded 1970 Buick GS 455 4 speed convertible and it is having a minor performance issue I am hoping somebody can provide guidance on.
I have fill the tank with a combination of 9 Gallons 93 Unleaded, 9 Gallons 100 Unleaded, & 2 Gallons of 110 leaded. When I drive the car without putting in the secondaries in (4 barrels) the car drives fine. When I start to push the car for more it starts to struggle - you can fell it wanting to go but it sort of goes back and forth a bit. When I really step on it and put the 4 barrels in (which sometimes seems to stick) the car starts to buck and pull back and forth.
what can it be?
Dirty fuel filter?
bad spark plugs?
What would somebody suggest doing to fix the issue?
Wanted 1959 Buick Electra 225 Convertible