I have had the occassional backfire through the intake with the underseat filter, undertank filter and triple filter, all when just blipping the throttle a bit. After a custom dyno tune, it still does it on occasion and like I said earlier I know I am running at 13.5 to 1 A/F ratio so I am not lean. If you do a search here or other rocket forums you will find others reporting the same. In fact that is what probably caused the infamous Uni-filter fire of 2006.
The afterfiring issue was somewhat easy to resolve because it was with closed throttle positions. And richening it up at lower RPM ranges and closed throttle positions is what solved it. However get too rich at small throttle openings and the bike will get very jumpy and difficult to ride at parking lot speeds.
When you blip the throttle you are in the F maps probably about at about 25% to 50% throttle opening so adding fuel at lower RPMs won't help. I don't think you want to add a bunch of fuel there because once again it will have adverse effects on other riding conditions. An accelerator pump would only benefit at WOT anyway. The PCIII has an accelerator pump feature but my dyno tuner didn't recommend it.
If anything it might be related to a timing issue, however I think it is just the nature of the beast. However do some experimenting. There were several times I had to push my bike back to my garage because of trying to resolve one problem and I ended up creating several more, that is part of the fun.
