If you really wnat to increase your gas mileage, you need to find what conditions your bike is happy at.
"Fuel atomization" is the key to efficiency. Fuel will always atomize better when the manifold vaccuum is highest (On carbureted models)
What to do: Get ahold of a vacuum gauge and mount it on your bike and hook it up to the manifold vaccuum port line that opereates the
AIS system.
Under all speeds and conditions your vaccuum will drastically change depending on throttle position AND engine
rpm's.
If you are pushing a severe headwind in 5th gear at, ...say 60 mph, your vacuum may be low because the engine
rpms are low and your throttle is 1/2 open or so.
If you downshift to 4th gear and raise your rpm's you may be able to cruise at the same road-speed with the throttle only at 3/8 open insted of 1/2 open.
Your vaccuum gauge will tell you which is better for the highest vaccumn equals better efficiency.
It would seem that an engine at lower rpm's would use less gas than if it were running at higher rpm's, but if your vaccuum (fuel atomization) is poor, then your combustion will be innefficient due to large amounts of fuel droplets not being burned properly. (The engine may have to "work" harder in 5th than in 4th when pushing wind at around 50 to 65 mph.)
Just something to think about if you care about your gas mileage on your vehicles or bike.

-StarMyram