How did you get 6 gals in it. It only holds 6 gals. When gauge shows empty on my 2010 FLHTK it only holds about 4 gals. Son-in-laws 2012 will hold 5. When stock both got 35 to 38 around town urban area. On interstate at 75+ would get 36 to 38. On back roads 38 to 44. Just don't go by the gauge. Unless you push it into the gas station I don't think it will hold 6 gals. It probably didn't get filled all the way up if you bought at dealership either. I have never heard of a stock harley getting that poor mileage. Get it checked.

 

I assumed my tank was a 5 gallon tank. The most I have ever put in was 4.5 gallons.
After filling I normally get gas at 140 - 150 miles around town before filling again. So right at 38 or less miles per gallon. I have not had an opportunity yet to run a full tank in 6 th gear yet. The few times I have got some time with 6 th gear it does go up to 160 plus. Being fuel-injected I am not in a hurry to run it to a stall to found out what it will hold.
I normally go 30 plus miles after the low fuel light comes on.

 

I generally ride at 65~70 on 2 lanes.

My MPG measured over thousands of mile was 44 MPG bone stock.

currently 43 MPG with 2009 FLHTC, hi flow intake and exhaust, nightrider.com xieds for tuning compensation ( so mixture about 8% richer when cruising).
Again, measured over thousands of miles.

as referenced above, keep the revs up!

lower revs does not equal most efficient operation- and the oil pressure and volume are rpm dependent.

lugging the Harley motor will destroy the bottom end bearings

I'll hit 6th at about 65 MPH on a level road with little headwind.

Mike

 

If it's a 2007, then it is a 5 gallon tank. Harley went with the 6 gallon tank in 2008.

 

My last bike had a modified tank. It normally would get 35 to 40 miles per gallon, but would get up and go. So the 3.6 gallon tank was annoying. I modified the tank to hold just under 7 gallons. I would go over 200 miles before going to reserve. Then a good 30 miles on reserve. I would love a 6 gallon tank but my tank has an awesome custom paint job.

 

36 Tanks of gas my average as been 37.49 mpg
High as been 43.82 mpg
Low as been 31.68 mpg

Lows were recorded running 80+mph
Highs were recorded running -65 mph

Gas mileage got marginally better doing a Stage 1 kit from Fuelmoto.