Two strokes are where you really have to keep an eye on jetting, you don't often pull a spark plug out of a 4 stroke and find aluminum electrodes! In my experience changing exhaust systems on a four stroke usually cause minimal changes in mixture. Subtle enough that I don't think anything will be detectable except by looking at the plugs or running an EGT. Exhaust gas analyzers are not often found in my roll around!Not sure if I know more than you Exavid, you know your stuff when it comes to Gold Wings.
The only thing I can say for sure is that you don't just rejet because you changed the exhaust. You have to read the plugs as I described above. EFI will definately compensate.
I've seen some headers and mufflers that need the carbs leaned out and others where the carb needed to be richer. Only the test will prove it out.
Exavid said, "Two strokes are where you really have to keep an eye on jetting
I've got about 800 hours flying Ultralight and Experimental aircraft powered with 2 stroke engines, Mostly Rotax but a few others. These engines routinely operate at 65-75% power so jetting is CRITICAL. Almost all installations include exhaust gas temp gauges as well as cylinder head temps on the air cooled units. Two strokes rely on proper jetting for running right but also use the fuel mixture for part of their cooling, carbs are designed to run leanest in the upper midrange and richen up a lot at full throttle. The amount of jetting change you will need on a GW is pretty slight with the exhaust systems available since they don't vary the pressure and tuning all that muchYou've got that right on Exavid. I used to have a 2 stroke Kawasaki 750 H2 that would seize pistons almost instantly if I made any changes to the expansion chambers or air filters.4 strokes are far more forgiving.