I learned when we started the dyno run that my 55 w/ bleed holes pilot was way too rich at idle with stoichiometric of 8-9 depending on mixture 1 full turn out to all the way in.  As for riding, at 1 full turn out (stoichiometric 8), I still get some quick loud pop backfirng when 1) shifting from 1st to second, second to third- both when revs are a little higher than other gears, 2) when cruising at a steady higher rpm such as going down the highway in 5th and roll off the throttle.  I know al of this is common for our bikes. However, by turning the mixture screw out to 1 1/3 turn total, I can eliminate all highway throttle roll off pops and get only an occasional, isolated low volume poof on some decels.  For all intents and purposes, I'd say the overly rich idle circuit eliminates the noises.  But at this setting, the engine starts to stumble when I come to a stop due to being too rich.  

Do you think removing a little of the richness from the idle circuit (screw in to maybe 3/4 turn) and adding it to the midrange (thinner spacer) would achieve the same level of backfire elimination as an overly rich idle circuit?  In other words, with my pipe, will a mildly rich pilot + a mildly rich needle position accomplish the same as an overly rich pilot?  
 
Edit: On the flip side, can you use the pilot jet/mixture screw settings that are required to eliminate backfires and pops as an indicator of the flow characteristics of a pipe?

Would you say a #55 pilot w/ bh and mixture screw only say a 1/2 turn out passes the same as a stock 52.5 at 3 turns out?  

Hows the white washer play into this? Seems if its been cut down or removed, maybe this would be a place for it to be thicker than it is now?