Start with controlling the opening rate as jake has already pointed out, another NHRA stock class method is to reaise the float level in the outboard carbs. (both of the with the mortor running )until the fuel starts to drip out of the venturi boosters and then lower the float level between 1/8 and 1/4 turn down Are these the stock 340 six pak carbs with the Po Max blocks or some other six pak carbs? Have you treid changing the center carb. pump squirter to a bigger one ike a #37 or bigger? If not try that also, it is easier to change and see instant results