I have a 2002 FXDL with the twin cam 88" and on the way to work the other day it started backfiring and sputtering badly. It cleared enough to get it home for some diagnostics. Found the rear plug was carbon fouled pretty badly. Got it cleaned up and re-installed. Bike now idles poorly and the back jug puts out a small amount of black smoke while the front one is clear. Swapped the plugs with each other and it still does the same thing, Only the back cylinder has problems. If this were a fuel problem wouldn't both cylinders be affected? I am going to change plugs and wires today to see if that helps, but I would like other ideas to look into. Baffled as to why only 1 cylinder is acting up.