I tuned both Harleys with a combination of plug reads, throttle response and an oil tank temperature gauge.
Going richer than factory brought the oil temp down ~ 20 F on sustained grades.
It also dropped MPG ~ 14 %.
I would look up posts on Sportster.org, to check my memory, but it ceased in 2012.
From memory, going up interstate 5 from Los Angeles with the 1200 Sport, stock was almost 60 MPG (1200 cc, dual plug heads, W grind cams).
Again, from memory, the same trip, after rejetting, dropped from 60 MPG to 52 MPH.
This was on a Keihin CV40 carb, with mixture at 2 3/4, pilot from 42 to 45 (0.45 mm), needle N65C (stock for 1988, with no accelerator pump) and 195 main reamed to 203 (2.03 mm). So it was made richer every which way.
BTW, both Sportsters were California models, the leanest of the three produced by Harley at that time (CA, 49 state and international), so base was very lean.
However, if too rich, the mixture can "wash down" the cylinder walls to dilute crankcase oil, darken plugs and send unburned fuel (black smoke) out the exhaust.
Riding to over 8,000 feet elevation, my TW performed very well with only a mixture screw adjustment (from 1 1/4 turns out from factory to 2 3/4 turns out from gentle seat)
Bottom line, how do your plugs look?
Does it seem to run any cooler?
Instead of hesitating, if it was lean, does it now blubber from too rich?
If any rich symptoms are present, I would first remove the needle shim.