Today I had the chance to answer a question that's been on my mind, how would my 04 RT run if I programmed lambda from 0.94 where the Wideband O2 has been (13.8) to a leaner than stock setting of lambda=1.06 (15.6:1)? The answer: Not Terrible.
After programming the LC-1 to the leaner setting, and then resetting the Motronic and removing the BoosterPlug, I ran a 10 mile test loop. At first, during the warm-up phase with enrichment by the Motronic and Open Loop, it seemed fine. But as I passed through 4 bars on the temperature gauge, it was apparent that the motorcycle was noticeably less responsive to the throttle. Then, fully warmed up, I started a climb through the gears, guess what? The motocycle surged around 3000 RPM in second, third and fourth gears--not a pronounced surging, just subtle modulation of the torque and shifting note at the exhaust. I couldn't wait to get back and reset to lambda=0.94.
So what did I learn? There is definitely an AFR component to the Boxer surging phenomenon: 6% leaner than stock is too lean for sure, and I know that 6% richer is great. Where is the spot in between the two ends that is just rich enough? Just a guess, somewhere between 14.0 and 14.4.