Go through the igntion and plugs, etc., and then run a compression test on all cylinders; with a steady miss like that, it is either ignition on one cylinder or a leak in a cylinder or instake runner. Is there any miss at idle?
Even your 4.5 power valve should have cut in with the pedal floored; changing from a 4.5 to 6.5 power valve won't change/cure a flat miss on one cylinder.
I had an issue with plug wires earlier and went threw all of that, wires, plugs, etc. That problem (rough idle) was caused by a bad set of wires that would push the connector into the boot instead of plugging in. I pressure tested each cylinder for leaks already but haven't done a compression test (that would be really rough on a few cylinders). No miss at idle, in fact after fixing the wire issue it smoothed out so much that it now sounds very mellow.
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I was going to say something in "ignition, my 1st wild as guess" {like your cap &/or rotor or even air gap if it has one} or advance curve even, or initial timing maybe,
valve-train somewhere {I know you don't want to think it's a bad rocker adjustments too tight/too loose, sorry},
possibly bad wire arching {need ultra-low resistance wires with a hot ignition system like less than 100-ohm's per ft loss, you could be getting cross arching between wires if not separated, adequately/properly}, wrong heat range plugs ??,
also with an aftermarket cam, they generally like allot more initial timing like 16*-20* BTDC easily,
do you have a vacuum advance & if so, is it adjustable ?? {a little allen head screw in the center of the pod thru the vacuum line port, limits the amount of added advance}, if so limit the amount of advance & time it to have between 32*-38* max total timing, usually towards the lower side...
Fuel pressure/supply, Jets, accel. cam & squiters could be lean/too small, if it was the acc. pump charge it should go away after initial hit, but if it's lean {jets or even wrong or bad power-valve} it will surge kind of, under a light load or when your on it hard, under a load... what kind of fuel pressure & pump etc. ??, is it "flowing 5-7psi" everywhere ??
sorry I'm not much help guessing here
I'm not allot of help either, I haven't had allot of time to trouble shoot it yet and can't even answer all of the questions being asked. I really started this thread to get all the idea's I can before I get back in the garage. Checked for arching the other night in the dark with a water mist like suggested and nothing, I'm running the stock recommended plug (for now), wires are Taylors (recommended for hot ignitions), already checked the air gap and I'm fairly confident that it isn't the carb now (idles great, responds well but stumbles threw the whole rpm range as long as it's under a good load but doesn't miss a lick if you accelerate very very gradually). I'm not a pro but I would think if it was the carb it would be more isolated to a particular circuit like idle, off idle, mid or wot but it's everywhere but idle. Thanks, I'll take note of all because even if it is the cap like I believe it is I still need to get it dialed in once this is resolved.