Observation: The Dyna S timing plate was rotated nearly ALL the way clockwise when I took it apart. It will start and eventually idle. But it hasn't been (by me) run on the road up to any kind of speed, since it's still on a lift. I'm guessing maybe the reason the PO had to rotate the plate that far is to compensate for the behavior of the 333 advancer? I'm thinking Tomshep's comment "You could find quite a bit more at the top end if you advance the 333 unit at the expense of lumpy response from 1100 to 1500 but it will be a good experiment." might be what I would experience if I put this thing on the road with that 333, and with the plate rotated that far clockwise.
Yep, you're getting onto it now..
The advancers are all interchanged for differing performance rates, and Dave500 is right on the nut when he states these are really a "retarder unit" instead of an "advancer" unit, as these engines would NEVER idle if the advancer was more than 15 degrees at 1000 RPM. The general overview goes like this: the full advance should arrive at the same time the intake valve closes against 'burnback' from the waste-cycle spark these engines have, which is the fuel-air mix burning back toward the carbs. The plug sparks in between exhaust-intake cycle ('overlap' cycle) due to the dual-coil design, which makes it imperative that the timing is not too far advanced while this happens. If it is too advanced, then this cylinder, which is just starting to take in a charge, can light that charge off, burning it partway as it also inhales it (burning it back toward the carb - 'burnback'). This lowers the power for that next power stroke, as part of the charge is already used up, and it is also heating too early and trying to resist the upcoming compression stroke as the result. The difference is dramatic when one that is advancing too fast is modified to either retard the spark totally, or slowed down until the charge can be 'clean' (not ignited) coming in: the engine always then produces more low-end torque.
So, I suspect the -333- advancer, with its less total advance, was probably used on a heavy machine like yours so as to increase the low end torque. It also sacrificed some higher-end HP, though, so installing an advancer that is slower but has more total advance angle is a good idea here, to get that power back again at higher revs. I would recommend using a -300- or -323- with at least 1/2 turn cut from both springs, or as on my own 750 engine with the fully hemi'd head and porting, 1 full turn off one spring and 1/2 turn off the other for full advance at 4000 RPM instead of closer to 3000. This will also allow for use of Regular grade gas without ping at any speed, even under heavy loads, which will bring out more torque until you achieve the RPM where the octane has burned off before the bottom-of-stroke: this is usually around 5500 RPM with the intake valve opening around 3-5 degrees BTC. If the cam opens later than that then this power cycle moves up in the RPM band (like in the "F" and K7/8 cams) to more like 6200 RPM, which is probably not ideal on a heavier machine like a trike. If yours opens later (worn cam chain components also cause this) then a slower spark advance is even more important for low-end torque. If you feel the top-end power is falling off around 5500 then step up a notch on the octane and try again until it becomes more linear: too much octane with too slow spark advance makes for a colder-running engine at lower speeds and fouls the plugs faster. Ethanol makes this worse, BTW, because it burns slower than pure gasoline...
