I am trying to raise the fuel mileage on my brothers bike. 2001 FXDWG carburated. It has the Harley replacement air filter, and Reinhart Bub 2 into 1 exhaust. Started out with a 180 main 45 low speed jets and the adjustable needle. That's when the mileage went down into the 20s. I tried the 185 main and 46 low speed with two washers under the stock needle. This set up made the bike hard to start after riding and stopping to fill up. Blew lots of black smoke after it finally started. Tried to adjust the fuel mixture but didn't seem to matter. Came home and changed the low speed back to 45 and adjusted it to 2.5 turns out. Went riding again mileage came back up to around 34 both of these trips were slower speeds 50-65. Bike would die after idleing a short time, but started right back up. We road on, the next fuel stop mileage was down a little to 31, this was more higway riding at 65. This time I adjusted the air mixture to 3.75 turns to smooth out the idle. I'm thinking about changing the main back to the 180 to see if the needle is coming up and letting more fuel thru than he needs? It seems like your not using much throttle at these speeds and most of it would be coming from the low speed jet. Am I missing something? The bike runs great no problem taking fuel, seems to be no surge or falter when you let off the throttle in third gear. Sorry I'm taking so long to explain but more info is better than none.