Chris It Sounds Like You Have Had This Trouble At One Time.i Just Took The Box Stock Holley,bought The Proform Main Body And Very Carefully,step By Step Followed The Instruction Sheet And Built It.no Jet Extentions,the Float Levels Were Left As They Came From Holley.its Not Dumping Gas Out Of Either Vent Tube And There Is No Black,or Any Smoke When It Stumbles.but It Does Pull Hard Like You Said,for Less Than A Second,falls Then Picks Up.is It Needing Extentions?floats Adjusted,power Valve?