Tommy;

Its pretty unusual for an electrical (ignition) problem to get getter when reving, so I would agree with the others that it's likely a carb issue...a couple of questions though:

Did the symptoms start just after the ignition tune-up? (If yes, you MUST also suspect the work performed, although I can't immediately think of an ignition probem which could cause the symptoms noted.)

Were the carbs well adjusted, and was the engine running well, and these symptoms develop, or were they never right? (This determines if you're doing a problem search, or starting with carbs at unknown settings.)

You say the engine is "stong when revved"...which also points to uneven idle (mixture) adjustment, but note: Reving is a fairly low load condition (engine revs are increasing but working against engine rotational inertia only) ...how does it drive (normal load condition?).

--------------

....so if are talking about an uneven carb set-up and synchronization here (and fouled 3 and 4 plugs, probably due to a rich mixture) I would also start by cleaning the fouled plugs, and reinstalling them...also checking throttle and choke linkage adjustments... remove airfilters, start, and first note the amount each dashpot is rising at idle...then also while blipping throttle...if possible, using flashlight, observe the relative amount of fuel being atomized at the carbs...make note of obvious operational differences and settings....use the daspot lifting pins to do a miixture check for each carb (although I only consider that a rough check, see below!)



Let us know how you make out!

Cheers