Whoever told you that needs to quit giving advice, stay away from Q-jets and go back to their "day job"!
The power piston spring controls the cut-in point for the primary metering rods. There were at least 35 different springs used by the factory and probably more. That's just how many different ones I've removed from unmolested carbs over the years.
I sell 4 different springs in a kit. They span the most ideal "range" for cut in points so folks can custom tune with them.
Tuning with PP springs takes considerable time because nearly any spring you use will be down at idle speed on most engines. They are in there to raise the rods when heavy throttle is applied and vacuum falls off. At the same time the distributor vacuum advance looses vacuum signal and the timing retards. So timing retards and fuel delivery increases at the same time whenever the engine is heavily loaded.
For the most part we want the metering rods to raise early and quickly for best throttle response when the engine sees a heavy load. Since driving conditions vary considerably it usually takes quite a bit of testing to determine the most ideal cut-in point when tuning with PP springs.
I can help you cut to the chase by recommending a PP spring for the combination. At that point the builder/tuner can experiment with the other springs I the kit to see which one works best.......
