I think that the demand regulator is something to keep an eye on, only takes one tiny particle to make it stick open. There is a needle valve that should only open when the carb pulls a vacuum.
The manual says do not dissemble but read that somewhere that it is quite easy to do so and it was successfully restored to a fully working condition after a good clean out.
I would suggest that the work area is very clean, almost surgery like and no harsh solvents used to clean the diaphragm, obvious problem area is the valve and valve seat area.