On an 05 Speedmaster, I hit reserve at around 135 miles, almost like clockwork. (I'd call that at 40 MPG, based upon a typical 3.X gallon fill up.) I'm a svelte 240 lbs, and still running a stock setup at around one month into ownership with a roadster windscreen. I do believe I'm running a 16 tooth front sprocket. My 1500 miles of ownership are mostly rural and very often into the gearbox so far, perhaps at 1/2 the time with my wife or one of my daughters as a passenger. I'm waiting on delivery of some 130 jets, an air filter, and an 18 tooth sprocket, and hope to make time to remove the AI & ventilate the air box and synch and adjust carbs etc., when we get back from vacation around the 16th. With any luck, I may be able to up the MPGs a bit after some modifications.
FWIW, with the AI still on and drawing vacuum, one pipe is yellowing, and the other is not. I'd want to believe the factory carb setup is less than equal at this point.
