I have a 2005 Deuce, 9000 miles, screaming eagle exhuast, air cleaner, and HD DOWNLOAD kit, installed when new, that just started spuddering now and then, there is also a vacum leak sound from gas tank. Sometimes the bike will run perfect with the sound. It runs the worst popping from trottle body, at slow cruising speeds, 15 mph. I have tried injector cleaners, and horsepower additives. The horsepower additive works the best, why? Can somebody help a biker out?