I have rebuilt the carby - but the throttle is very difficult to operate. The washer that attaches to the diaphragm seems to be impending movement. Any ideas?
It sounds like you have put one of the parts in upside down, in paticular the plastic doughnut with "this side down" written on it.
It has three parts sticking out which fit into the grooves of the carb housing. they must be slotted in.