Here's a good mileage test. I just took my bike from Pittsburgh to Ft Lauderdale and back. Total trip 2596.1 miles and the mileage calculation was completed to the last fillup at 2463.8 miles. Gallons used were 59.877 gallons. Mileage for the trip was 41.15 mpg. I was not expecting anything near this figure.
I have an 09 SEUC with D&D 2 into 1 exhaust, Zipper MaxFlo air cleaner, HD Super Tuner, Dyno tuned. No other mods. I was not riding the throttle easy at all. Cruising speed was normally around 80 mph with speeds in excess of 100 mph at least 20 times, and I couldn't even guess how many times over 90 mph. I did hit a top speed of 110 mph at one point, and it seemed like I still had much more left on the table. It was running very smoothly at that speed and around 3500 rpm's. I did set the bike on cruise control several times on the way back, at around 75 mph, but I have trouble resisting that crack of the throttle on the open highways, so even while on cruise control, I made lots of bursts to 90 and 100 mph. I was really expecting to see a mileage figure more like 34 to 36 mpg, so I was pretty impressed when I calculated this.
As far as filling the bike, I found that once the pump shuts off initially, I could still get another 20 to 30 quick on-off squirts of gas to top it off with the bike on the jiffy stand...probably lots more room with the bike upright. I was getting from 200 to 210 miles per tank before filling up when I was riding alone, and usually showed mileage remaining of 35 to 45 miles on the tank when I filled up. On the way down, when I was riding with some others, I was filling up at odd intervals due to when the others needed to stop, and one guy had a 2 gallon tank on a Sportster, which meant stopping for gas every 80 miles, or me filling up on every second gas stop.
Anyway, that's about as much info that I think I could possibly explain about the mileage. This bike really loves speeds of 80 mph and up. The only complaint I have is that the bike is pretty much uncontrollable with heavy crosswinds. I happened to hit some major wind issues on the trip heading south and had to pull off the road at one point and ride down the berm of the road for a few miles in 1st gear, as I almost got blown into the side of a few semi's through one wide open stretch. The wind was so bad that when I was at the big Daytona Harley dealer in Ormond Beach, FL, it took me a while to park my bike. I finally found a spot to park behind a truck to partially block the wind and even then I had to aim the front of the bike directly into the wind. If I parked it with the wind hitting the bike from the side, I'm sure it would have blown over. That's quite the dealer they have there. As you will see in the photo, I was about the first customer for the day, and when I left, they were pulling the bikes in from outside for the night. I was back and forth between Harley and JP Cycles the entire day.
In case anyone is wondering, the truck with the bike in the bed were there to be raffled off. Nice truck!