351c bogging when accelerating

When the car is out of gear it rev's just fine. No spit,bog just nice and clean. When I drive it and step on it, I get a bog. The carb is a 750 holley double pump,dual feed with mechanical secondaries. The jets are 76 front 80 rear with a plug in the power valve position. I'm wondering if the plug is causing the problem. The guys at the track said to use a plug and up the jets by a few sizes. What do you think? The float levels are fine and the accelerator pumps are set. The shooters are 28 front and 37 rear.