I own a 70 GTX with a 440-6. The secret to tuning the sixpack hollys, is to take the out boards and go to the base. You will see the idle ports are coverd over in some metal. Dig this metal out and behind it you will see the idle needles. Spray some form of solvent into the port and work the needles out. Move the needles until they are free to turn in and out. Put the carbs back on and use a flexable standard screw driver to tune the idle as it sets and runs. tune at least 3 times. turning them in until they stumble. Then turnout until the idle smooths. Once the idle is smooth the vac secondarys must be cleaned and made sure of no vac leaks. I also made sure the vac lines are the same length and attached to the right vac port. The car should perform now and you will get a blast out of the 4barrels coming in. I hope this helps. Randy.