With the butterflies closed, the idle circuit should be set to the highest idle speed/ smoothest idle. You may have to lower the idle speed adjustment in order to realize any changes in the idle speed using just the mixture screws..Once that is established as close as possible, (as exotic cams and intake/exhaust upgrades from stock sometimes make these adjustments tough to dial in). Be sure the accelerator pump actually squirts as soon as the throttle shaft moves the slightest bit, and the fuel should continue to flow through the initial opening of the primaries. Most of the holleys I've seen had 6.5 Power valves when new.. This is a ballpark number that works with most automotive applications, however boats aint cars.. As far as a starting point, 6.5 isn't far off. You will have to find out how your throttle response is, throughout the power range of your engine, and the demand of your hull. If the engine seems to stumble when nailed from a cruise speed, the pV may be too low, or the pump timing may be early or late. These fine tuning areas must be evaluated in the real world, under real use. It is a common misconception that there should be an abrupt increase when the secondaries open, this is wrong! The sudden jerk you feel is actually a bog, and a recovery. The secondary action should be a gradual increase in speed/power, a smooth transistion into WOT. And yes, the PV plays a role in this transistion, and you may want to monitor the vacuum as you experiment with your particular set up for a better idea what PV will work the best.. Some tuners just block them off and tune around them, but again, the real world, under real use is the only way I know to fine tune carbs/timing.....Just my .02 Moneypitt