here is how i set the power valve on my holleys: with the engine hot, i let the car idle IN GEAR and take a reading of the vacuum. that is most likely the lowest vacuum reading you will get. then i choose a power valve with 2 numbers less than that reading (that is the old fashioned-way but it works). that way, it will not open unless going wide open throttle or when accelerating. note that the number of doors (or openings) of the p.v. plays a big role when accelerating. a regular p.v. has 2 small holes from holley most of the time. going to a 2 door (2 rectangular openings) pv will richen up the mixture under acceleration. a 4-door pv will richen it up even more. also, make sure the p.v. you chose hasnt dried up, that would mess-up your calibration.
what i meant about more vacuum reading for a double-pumper is that it will make more vacuum than the current carb, if it is not running right. also, out of 3 vacuum-secondary 3310`s i had, only one was on par with a 750 double-pumper on my car.
also, if you removed the choke, there is a chance you have a vacuum leak where the choke mechanism was. mostly occurs on carbs with ELECTRIC choke beeing removed.
