The slide needle and its jet are supposed to control the midrange throttle positions. Note this is different than an RPM reference, due to the mechanical slide design. However, the main jet does also feed the slide needle and its jet orifice.
For adjustment, the main is usually selected first, as that supplies the maximum fuel demand at WOT under load. The slide needle and jet then uses what is available from main and further meters that to supply needs at mid throttle positions.
All the above bleed some at idle position, as the slow jet does at higher throttle positions. So, there is some interaction among the fuel metering devices. I set the idle mixture last, so it will work well with the other settings best for road operations.
Carbs are dumb to the engine needs. If exhaust design or induction design changes from what was delivered stock, stock settings unlikely apply. And, the new configuration needs must be compensated by changes in carb delivery.
For the idle chop. Must be at op temp and idle long enough to show a deposit pattern on the plugs. If too rich, it won't take long, if you are too lean, it will take forever. For practical reasons, you wouldn't want the plugs to load up at stop lights, or after, say, a 5 minute idle. If it does, you'll be blipping the throttle repeatedly to keep the plugs clear for the green light event. Lots of Harleys need this.
Cheers,
P.S. It's really a shame about your underfed crabs. I've been able to avoid them all my life, though.
