Thanks Chris. Very interesting info. I always wondered why that that little vacuum device only went to the front cylinder and what would happen if it were hooked up to both. My 650 runs smooth as silk, no hesitation,surging,or stalling. just the on and off vibration. The symptoms of a misadjusted TPS on a car anyway are hard-starting,hesitation and rough idle. Thankfully I don't have any of these problems so I will leave it alone for now. The balance or amount of air being drawn into both cylinders is dependant on engine temp. I wonder if varying valve gaps between the two cylinders associated with constantly changing operating temps changes the balance enough to be felt, temperature basicly changing the sync constantly. If running a hose between the two cylinders would help this condition it's definitely worth doing. Probably the only thing I miss about my old Sportster was the single carb and split manifold feeding both cylinders, very simple to tune. Dan