Join Date: Dec 2012
Location: Gastonia, NC - Born & raised in Connecticut - 31 years
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Agreed with above - do the basics first. Compression test & adjust valves - zero lash using polylock rocker arm nuts, ensure you have a free flowing exhaust system and no collapsed mufflers or restrictions (check the exhaust manifold heat riser if so equipped). Good gas, tune-up, rebuild/tune the Q-jet, adjust the timing curve for best performance.
Often, the secondary air flap on the Q-Jet does not open soon enough or has been adjusted too tight. I would make sure the air flap is snapping open, but not too soon as to cause the engine to bog - that's how I adjust them. Getting this correct is very important to engine's power and responsiveness.
If you do not already have it, suggest you invest in Cliff Ruggles book, How To Rebuild And Modify Rochester Quadrajet Carburetors. It will show you the small set screw, spring, and the screw to adjust the tension on the secondary air flap, as well as the vacuum diaphragm (which I always tossed away) that pulls down on the air flap.
Once you feel you have the engine performance tuned, then if you wanted to play around with other items to improve HP, then I would look into other add-on items.