ORIGINAL: Stickbuilder
One other thing, When you had the pump apart, did you lube the diaphragm? Sometimes they dry out, and It could just possibly be that you are not getting sufficient movement to pump at low speed. a very light film of petroleum jelly might do the trick. You might want to gently rub it into the material.
I now have taken the motor to the LHS and parts are on order, There seem to know what is wrong, only problem parst are hard to get. I'll let you know what comes out of this.
roltech