<<<Float height is set perfectly, by the Amal GP tuning sheets.>>>

Pete, how are you checking the fuel level. If the float chamber has a fuel level mark on the outside, these can't always be relied upon to be correct. I always use a piece of clear tube from the outlet on the chamber, so the exact level can be set, viewing the fuel in the tube, with the reference point. ( base of the circle on the air jet plug.)