Recently acquired a 1994 FXDWG with mileage at 20,000ish, and as far as I know it's completely stock. While tracking down an annoying rattling noise, I pulled the front exhaust pipe. Looking in the head, I can see that the valve is white..and by white, I mean "frosty" white. I'm assuming that this is from running at an extremely lean condition. I checked and plug/cover for the carb mixture screw was missing, so at some point, someone had been fiddling around with it. I replaced the spark plugs on bringing the bike home and 700 miles later, they appear to be burning properly..light greyish..no blistering or white flakes. The white valves really came as a total shock to me, because this bike runs 100%....starts..idles..excels..cruises..all EXCELLENT. However I did notice on two or three occasions, on deceleration, there was a single "pop" from the carb...this was in the 700 miles I've put on it. At the time, was thinking the pops were from the very cold air I was riding in. Man, I hate the thought of monkeying around with something that runs so strong, but the white valve does have me concerned. So, my question for the more knowledgeable.. should I crank out the mixture screw slightly..or maybe a larger jet? Any info would be greatly appreciated.. Thanks! Oh, and the rattling noise turned out to be a broken muffler bolt..replaced it ,and what a much more pleasant ride experience!