Powersports customers have a right to be concerned with fuel economy. While motorcycling may not be able to justify itself on the basis of fuel economy when speaking of anything larger than a scooter, it still counts. And when an indvidual machine is fueling poorly, it really counts! One thing those who have not spent the bulk of their working lives in the powersports business may not be aware of is that powersports manufacturers have with rare exception traditionally avoided the subject of fuel economy, for some pretty good reasons. The biggest single influence on fuel economy for a powersports vehicle, what muddies the waters the most and sets powersports apart from all other wheeled vehicles, is something called user-to-vehicle-weight ratio. The weight difference between a 150 pound driver and a 250 pound driver won't make a dent in a full size pickup's fuel economy because the user-to-vehicle-weight ratio is so high. The 100 pounds does little to offset the weight of the truck. But take a 500 pound motorcycle and that same 100 lbs., and now you have a different scenario. The difference between the 150 pound rider and the 250 pound rider makes a much more significant difference in the motorcycle's capacity and loading, hence in its fuel efficiency. This one factor is an important if not the most important single one at play when it comes to fuel economy. And it's just the beginning. Add to this individual rider preferences for use of the throttle, which gear the rider is in most often, road surface types, road grading -- that is, incline, which is huge -- and much more. Taken together they all add up. Now you have so highly subjective an issue that you can see why powersports manufacturers have avoided discussing it for as long as anyone can remember.
So there are many considerations, all valid, and user-to-weight-ratio is king. There is another thing folks often overlook however, and it is just as important as user-to-weight-ratio, and actually more important and more pertinent to the rider who more or less suddenly experiences a change in fuel economy. And that is chassis maintenance. A few years ago one of my customers had me do two sets of identical carbs for him (not unusual). They were both from the same model bike. Yet, when he got them back and everything was equalized fuel wise and carburetor wise, he complained of a 25 percent difference in fuel economy. After going over the basics, it was finally determined that the poorer fueling bike needed its drive chain lubed, and thereafter its fuel economy matched the other machine. That's all it was! Chain maintenance! Hard to believe? Not if you have worked around a horsepower dyno for any length of time. Dyno runs frequently show up poorly maintained drive chains. That and wheel bearings, tire pressures, and dragging brake calipers, with the latter, brake calipers, being right behind drive chains as power-robbers. Food for thought?
Here's one more piece you may not have thought of. Sometimes a clogged carburetor fuel passage can be responsible for poor fuel economy. Come again? A clogged passage? Yes. When a carburetor circuit is working less efficiently than it should, we tend to compensate, that is, call for more power -- how? By using more throttle, of course. And it's this additional throttle opening that uses more fuel, because it brings more carburetor circuitry to bear on power output than was necessary before. Hmm. Interesting. And as you would expect, this works in reverse, too. In one of the few instances where I recommend jetting up from the stock spec on carbs for better performance, you will find that there is no fuel penalty in most cases because with the revised jetting less throttle is needed to get the same power. It's real.
To recap, don't think of absolute fuel economy, that is, "it's a 750 so it should get this many miles to the gallon," to be an emperical reality. Within reason it just isn't. You can't count on it, for the very subjective use reasons we have explored. The kind of fuel economy measureements that matter are those that are strictly comparitive, that is, when the same person rides two of the same model bikes under the same conditions. Everytning else is out the window. Remember also that some not-so-obvious things affect fuel economy. Chains, tires, and brake calipers, for example. Finally, don't overlook the non-intuitive fact of dirty carbs in producing poor fuel economy.