Last night we did the change. The bike originally ran poorly at part throttle (2 -20% between 2K and 4500 rpm). Lots of surging displayed as very rich mixtures in that TP & RPM range. We cut the fueling back to run at ~ 13.2:1 in those areas. Much smoother and very rideable and wants to accelerate at a touch of the throttle. The problem with the popping began there. String of firecrackers noise coming from the pipe during decel.
We originally addressed it by adding 8% fuel @ 0% TP from 6000 down to 2000 rpm. Seemed better, but we continued to experiment. We settled on 8% from 6k down to 4k and 11%from 4K to 2K. 15% fueling at 0% throttle seemed to make it go back to a worse pop condition so we went back to the 11%. If you've tuned out decel pop on the past, you know the routine, so there's no need to give the crazy details of how we arrived at these numbers. There was still a hint of popping but it was much better.
Riding on hot days under real conditions showed that it was still there. Reduced, but still present and more annoyingly, there was a loud pop or sometimes a double-tap at 3500 rpm. Oh, what to do?
Last night we went with the theory of cooling the exhaust/drowning the pop with richer mixtures. So we added 4% and 8% to previously tuned cruising and back road riding throttle positions. We had success. The decel pop became a low toned growl or burble. You have to hear it coming from that slash cut to really understand it, but the sound is unusual and kind of cool to be honest. You know there's something different pulling up next to you. Unfortunately there was still a bang or double tap at 3500 rpm. I took the bike out on the road (no dyno necessary for what we were doing now) and found that the pop rpm was very repeatable. It happened at the same rpm regardless of prior throttle position. Meaning you could be decelerating from a large throttle position - high rpm run up, or just decel turning into a right hander and dropping one gear from small throttle. Oddly it seemed worse in 3rd gear so most of the testing was done at that gear/rpm combo.
The final stab was to throw fuel right at that rpm point. We added 20% more fuel at 0% throttle from 4k down to 3500. The pop and double tap disappeared. It only showed up once during the test ride as opposed to every time we swept through that rpm range at zero % throttle. Keeping fingers crossed, but cautiously optimistic that we've arrived at good rideability and minimal noise.
Thank you to all those who offered thoughts and tips. I figured I would share back for anyone who has similar situations.
Last edited by cwalker2; 07-06-2016 at 11:52 AM.