Hi MO,That's good but I probably should have been a bit more specific. I was thinking mechanical/vacuum advance .. wasn't sure what you have going on in that regard or if you've looked at it as part of the overall equation.Regardless, I would still mess with the power valve. With your vacuum readings that 3.5 valve is likely opening too early, which can for sure cause a lean under load issue.Oh and RE: testing a PV ... pretty sure if yours was bad you would have a rich idle and issues adjusting air/fuel mixture. Those are the classic symptoms. I used to work at an Andy Granatelli Tune-Up Masters back in the early 80s ... not sure if you remember that chain but we would actually advertise that a carb overhaul (if necessary) was included in your $49.95 tune-up! Needless to say, did many a power valve change under those circumstances... :-pGood luck!Jim
On Thursday, June 29, 2017 at 1:47:48 AM UTC-4, MO wrote:Thanks Jim. Some time back , a very good mechanic took my car out for a test drive for another issue. He adjusted my timing and it starts and runs very well. I actually never checked to see where he has it at, but with points, my dwell is right on--so I would guess the timing has not changed.The carb is not loading up at idle, and no black smoke out the tailpipes on hard acceleration. If anything, it may be too lean. .......................MO
On Tuesday, June 27, 2017 at 8:41:09 AM UTC-5, JimJablonski wrote:My 2 cents (and there are fellas way smarter than me in this group):- Get the right power valve, but as a baseline I would go with 5.5 not 6.5- Get the AF adjusted properly if you admittedly haven't; it is possible it is running rich at idle and loading up, which could be contributing- You didn't mention anything about timing advance ... to me this is part of the overall equation...Thanks,Jim
On Tuesday, June 27, 2017 at 2:24:46 AM UTC-4, MO wrote: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. .............................