Bit of an update. The 2" pulley did not have enough surface area and would slip when the pump was idling, probably a combination of diameter and material(aluminium.) I have since changed this to a cast iron pulley of 3" PCD and much better outcome. The speed is slower, however I made a simple throttle lever to increase speed to circa 750rpm and the line speed is in the range of 4.5 - 6m/minute which is fast enough for what I use it for, and it will do this all day without effort if required.