by Warkton Tornado No.1 » Mon Dec 03, 2018 8:31 pm
As I am always cynical of the standard bellows coping with even a moderately tuned engine, the first thing I would ask is if your engine is absolutely standard & as originally built.
If it is as OEM, then I'd suspect that your carburation is too rich. The body, slide & jets all wear & the consequence is that the fuel/air mixture becomes richer.
If the engine starts from cold with no choke, or it dies if the choke is left on (to cause a fast idle whilst warming up) then it could be that the MA18 needs rebuilding or changing, though I know that the float needle set up on the early carbs can cause richness on their own through allowing inaccurate metering.