4 on the floor, On slide valve cycle carbs and SU's and Hitachi's used on cars,the lack of an accelerator pump is due to the variable ventui design.This feature keeps the air flow through the carb at a high enough velocity to keep good atomization and generally prevent leanout when the throttle is opened up fairly quickly.Many Japanese 4 cylinder cycles use a constant velocity design, the slide is lifted by vacuum like a car SU. But the slide isn't controlled by engine vacuum below the throttling device, but vacuum created by the carb venturi.The Venturi principal is what draws fuel from fuel metering circuits on all carburetors.Only the idle circuits are directly linked to engine vacuum below the throttle. Large 2 cylinder carburated sport machines like Ducatis and Guzzi, maybe BMW's have accelerator pumps on slide valve carbs.Thet have large carbs, a sudden snap of the throttle will cause a lean mixture, making the pump necessary.The short intake manifold length on bikes helps also.I'm pretty sure this is correct, But, I ve been wrong before,lol.
If you have 4 38 mm carbs on your 70's 750, you got one hell of an engine to handle those carbs,I believe the stock 750 carbs are around 26-28 MM, with 30-32's used for racing.
