So far I've put street tires on it, filled it with 5W-30 Mobil 1 oil, reduced the idle speed, removed the brush guards, and overinflated the tires. I coast rather than use engine braking. With careful driving after these mods, the mileage went from about 48 to just over 50 mpg, maybe 52 on a good tank.
The mileage doesn't vary much, regardless of whether I drive on the highway or in traffic. I don't understand it.
And I don't understand why a single cylinder 650 cc bike would get such crappy mileage. Harley Sportster 883 twins are rated 57 mpg highway. Shouldn't the smaller, lighter bike get better mileage?
I'm stumped as to what to try next. Anybody know of closed loop EFI for motorcycles?
Capitalism: The cream rises. Socialism: The scum rises.
I think the big problem with motorcycles is wind resistance. If you were to put a very slick fairing on it I'll bet you could break 70 mpg. Still, motorcycle engines tend to be high performance and tend to suck gas. My Honda CX500 gets 45 mpg which is less than my Suzuki Swift car with an engine nearly 3 times the size.
Bike engines are pretty high-strung, so they tend to get bad mileage. Rich mixtures and very aggressive valve timing. If you want to mod it, start with cams. Harleys are 2 valve, and they aren't about max horsepower (at least stock), so they naturally get better mileage.
Air resistance is a huge factor on bikes, but it gets hidden by the motors. The best I've heard of was to take a Ninja 250 and swap sprokets: nets 90 mpg if you ride carefully. The sky is the limit with aero shells.
make sure not to lug your engine by running it to slow, I have a vacuum gauge hooked on to my honda cb125 and have found that haveing it reved pretty high, 7,000rpm (9,500rpm red line) seems to yeld the best results as it takes advantage of the agressive cam that is designed for high revs, and the throttle is hardly cracked open.
I'm running amsoil 10w40 synthetic motorcycle oil in my motorcycles, because the friction modifiers found in some synthetics can soak in to the clutch plates and make them to slipery to grab, but mostly I think that is aditives like molly.
making sure you have the stock air box on your motorcycle is something that alot of people make the mistake with, normaly when you remove the stock air box you reduce how consistant the intake vilosity of the incoming air is, and it screws with yoru fuel air mix, and from what I've found, if you want to increase your air intake, replace your paper filter with a foam filter.