I get a consistent 44-47 Supertrapp SE, TV111 and Doherty PowerPacc at right above sea level on my recent trip out west in the elevations got over 50mpg with 3 tanks in the 55-57 mpg range fully packed riding at 70 mph. That with 87 octane all they had at several places, bike ran great just like the car less octane less power.

 

It is possible to get the advertised mileage but conditions have to be just right. The higher the elevations, the better the mileage.

Even on my 120", I can get close to 50mpg at elevation, but real world is about 42mpg at 65-70mph here in northern Ohio and about 40-42 not on the interstate, but can also bring it all the way down to 32mpg if hammering on the throttle in town or running at 80+mph on the superslab in a headwind. I have found that the "10% ethanol added" does return about 2mpg less.

 

On a July trip to AMA vintage bike days I got between 39 & 47 on my 07 RKC, riding between 60mph & 85mph. One tank I got 34 with a very strong head wind on the interstate...47 was my best.

 

My last tank was 41 on the highway but into a head wind and traveling between 75-80 for quite a stretch.

 

I have gotten between 37 and 38 MPG on just about every tank I have checked since I bought the bike. An "08 Ultra that is stock and running the XIED'S. I have 5500 miles on it and that is a combination of in town and highway riding both. Doesn't even seem to vary much even with my wife on the back.

 

On 2000 RG I get 36 to 39 at 60mph on the interstate I get 31 to 33. I have a pc111 and blackjack slip ons. It is turning 3650 at 70 mph. It has very good power for a stock 88.
Tuna

 

Wow! You have very low gearing and that's why your stock bike feels like it has good power. Stock gearing (3.15) at 70 would be about 2900rpm. 3.37s would be about
3100.

 

Modifications will effect that number heavily also. Pipes, stage 1, remap, cams, etc....it all has the potential to erode your mpg results.

 

Got 50+ on my 05 RG with stage 1 and Kerker mufflers. Getting an average of about 40 on my 08 Ultra bone stock. Will change out mufflers with 1.75" baffles and no other changes and see what affect that has.

 

On my recent 2,800 mile Sturgis trip, overall, I averaged 43 mpg. High of 48 and low of 37. This is with a 103", SE255 cams, and SERT. I was pretty pleased.