Years ago a buddy installed a portable A/F monitor on his flatttracker ATK and was very happy with his tuning result.
The May issue of Motorcycle Consumer News has, on the back cover, a glowing write-up of the NGK Powered AFX Air-Fuel Monitor.
Dave Searle at MCN states, "Air-fuel ratios by themselves are not the final answer, but they're close, and from that baseline, additional dyno or stopwatch tuning to totally perfect the setup will require less time and money." My thought, exactly. I'm guessing the tuning arrived at using one of these devices is satisfactory for 98% of DR riders.
Reading some of the anguished emails from riders soliciting tuning help makes the $260 cost a cheap investment for mental health.
Searle states 13:1 is the optimal A/F ratio for power and cooling on the DR.
The older I get, the better I was.