You've done all the right things but did you clean out the carb? Old petrol will gum-up the jets, the drilled galleries and the float needle and its seat. un-screw each jet and hold up to a light, you should be able to see through it, if not, you need to clear it out carefully, same goes for the float needle, should move freely in its seat(when attached to the float) and have NO marks on the tip, the seat should be clean & un-damaged, worth getting a can of spray carb cleaner-it dissolves that hard-to-get-to gum that may be inside the drillings in the carb body.Good luck.
crabbiepattie
July 2010