I have a 2005 roadstar 1700 with the stock Mikuni BSR40. I changed the exhaust to the "Road House" duellys and the air cleaner to the "Max Air".

I now am running too lean as evident by the spark plugs, and more so by the sneezing/hesitation while accelerating from a stop.

I've already adjusted the primary mixture screw to it's limit, and slightly opened the choke/enricher cable.

I've heard that the next step would be to re jet the carburator, but I don't know to what extent. Do I need to re jet or might it be something else?

I guess you would have to jet larger, if it were me I would try a couple of sizes bigger at first and continue to plug chop. jets are way cheaper than pistons and much easier to replace.