There is no power difference using "K" or "P" metering rods at heavy and full throttle, as the tip size on either one is .026".
Used in .072" main jets, the 52P rods would allow .042-.052" of the upper section in the jet at light throttle cruising.
Using 43K rods you have a range of .039"-.043" in the jets cruising or any other high vacuum situation.
If using .072" main jets, you will have a broader range of control with the APT with our custom .044" metering rods, as the upper section tapers all the way down to .026", and is .044" at the greatest diameter with the APT fully seated.
Some tips on tuning. Choose the jet size first, based on heavy throttle power/performance without using the secondaries. Climb some steep grades at heavy throttle on the primary side only and change jets until you have the best power.
Install a set of tapered metering rods just over .030" difference than the jets size. For .072" main jets, .044" metering rods would be perfect.
Adjust the APT at apprx 3.5 turns up from seated, or use the "tip-in" method described in our book.
Do some extensive driving at light part throttle, and fine tune the APT screw for best transition off idle, light throttle power, and fuel economy. This may take several tankfuls of fuel to find the ideal setting(s).
Rarely does going really lean with the APT screw delivery best fuel economy, or power, unless you are driving strictly at freeway speeds on flat roads with very light load. More often than not, richer settings yield the best fuel overall fuel economy as the throttle angle will be lower for most driving situations.
Don't forget about the vacuum advance, it is equally as important as the carb setting(s) to find the best fuel economy. Lean mixtures need more lead time (advance timing at light part throttle) to be effective. You may have to add more timing in conjunction with leaning up the APT screw to see improved results......Cliff
