TwoTired ; Yes the mixture seems to be rich at idle, hence the increase in rpm's as the gas runs out. Rich enough to soot the plugs. When I try to adjust the idle mixture, starting at 1 complete turn from closed, I can get some increase in idle, but only to 1.5 turns then no more improvement. My air screws have been modified to close the hole that is ther on most if not all new idle screws. My line of reasoning is because the idle gets higher as the fuel runs out that the mixture is getting closer to Perfect !
True before it transitions to too lean.
From what I've read, a person tunes the carb to get the highest rpm that can be gotten at idle meaning the best fuel/air mixture.
True for "modern" carbs like the PD's used in 77 and 78, later CV carbs in the early 80's. But, the 750's PD carbs have accelerator pumps to shoot gas into the carb throats when the slides are raised. Without the pump (as in your early style carbs), it must have an over rich idle, or it will stumble badly when you twist the throttle, especially so when the engine is under load.
The pods have severely changed carb throat vacuum, reducing it, and this make the carbs draw less fuel from existing jets. The big pilot jet and the modified air screws were attempts to get the pilot circuit to provide more fuel with the reduced vacuum. It's a balancing act. If you are reading the spark plugs correctly as truly too rich, the cumulative mods that were made to them probably went too far. Engines are more forgiving of over rich than they are for too lean, which is why most bike modifiers think way rich is THE answer, I expect. It's hard to tune by sound alone.
The prescribed method is with an engine/chassis dyno and a fuel map from a sniffed exhaust.
Alternately, a test track and several sets of clean plugs, a stop watch, and lots of patience with successive tweaks.
Or, trial and error until one gets tried of twiddling it.
Cheers,
