I'm guessing you have a Yanmar 3gm, but they are all similar. White smoke while cranking can be unburnt fuel, ours did that and we had the injectors rebuilt (and then replaced). That helped the hard starting and reduced the white smoke. Another thing that we have used recently that seems to help is something I read here on Sailnet. Pull your stop cable out and crank for 10 seconds and then push the cable in while cranking, usually fires right up. Hope that helps.
SV Laurie Anne
1988 Brewer 40 Pilothouse