Bike runs really well apart frpm a little decel popping downhill. 

Running carby Evo with big sucker type intake, main jet 185, slow jet 48, mixture screw 3 turns open, float level checked normal, SE3 cam, Daytona Twin-Tec ignition, V&H big radius pipes. Only use choke first start in morn for 30 secs.

The thing that puzzles me is rear plug has more soot than the front, could it be that sucking air from around intake manifold at front cylinder making it leaner? I detected only a very slight leak at intake at both cylinders by using CO Contact Cleaner flammable spray - engine idle slows only slightly (however probably every second Evo has some sort of intake leak). 

Any thoughts?

you might be riding slow in traffic? or not keeping rev's high enough. could try to get a 46 low speed change main to 180.