As far as how many cranks to start, it helps to know how long BETWEEN starts. My car takes that if it's been sitting for a few weeks, but she fires right up if it's a day or so.
The stumbling may be signs of a vacuum leak, either at a hose, possibly the intake manifold gasket, or as Will suggests, a carb issue. If you can detail some more parameters, maybe some of the more experienced guys (which, unfortunately doesn't really include me ) here can help you out. Good luck.
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