I have thunderbolt IV ignition no points. After a high speed run the plugs are pure white Which would indicate a lean condition.
Carb was rebuilt this spring. Left it soaking in carb cleaner for a week. Blew out all the passages. Carb worked good and a non vortec engine
Gonna go with everyone else something else is going on. If its starving for fuel then the carb is plugged or something else is going on.