Right now, my average is 40 mpg (17km/l), 200 miles (328km) to reserve, this is surface streets and urban expressways .
I can do better on rural interstate highways, if I keep the speed down to 60-65 mph (98-107km/h), it's about 45 mpg (19km/l) .
But at posted speed limit of 75 mph (123km/h, 36-38 mpg (15-16km/l)is more the usual .
I lost at least 5 mpg (2km/l) when 10% ethanol was added to the fuel supply here in Phoenix, back in 2002 .
When the national speed limit was 55 mph (90km/h), and no alcohol in the fuel, I could average low 50's mpg (22-23km/l) on rural interstate highways .
With 83,000 miles on the bike, I wouldn't be surprised if the compression is down from a new engine .
Also the '81 R65 is jetted the richest of the twin shock R65's .
I need to find the smaller jets that I got with the '84 LS, I think they are 138's the same that came with the LS version bikes, the jets in the '81 are 145's .
The 1150 oilhead, gets 48 mpg (21km/l) in the usual city commute, and 58 mpg (25km/l) at 75 mph (123km/h) on rural interstate highways .