I've got a 2005 Spirit 750, chain driven, stock front sprocket, 38 tooth in the rear, Vance & Hines exhaust, K&N air filter, fuel adjustment screw was turned 1/2 turn to get the popping out. With or without windshield I'm getting 43 mpg. My cousin's Yamaha 1100 and uncle's gigantor Harley gets 43 mpg. I really thought I would get better than that. Anything I can do to get better?