I am trying to figger out a stumble in my Holley 4250 with mechanical secondaries--750 CFM. Low gear, rolling at idle, punch the throttle and get a substantial hesitation--not really a bog. about 1500 RPM at full throttle it takes off like a striped a**ed ape!. I think I have plenty of accelerator pump now. I put a 2.5 power valve in because I thought I had low vacume ..my bad. I put the vac gauge on and actually have 12.5 inches at idle. Do I just put a 6.5 power valve in, or is there a better way to know which PV I should use? BTW the engine idles fine, but I have not fine tuned the idle mixture yet. .............................MO