I would check the choke adjustment: too tight or too loose. Even a warm engine can benefit from a small amount of choke. Too little may not be noticable except by needing a few more revolutions to start; too much could give the same result, although black smoke after starting would be a strong indicator of too much choke. Fuel volatility can also be a factor if the condition mostly occurs during warm/hot weather. If that is the case, there isn't much you can do about it, because fuel blends are pretty strongly regulated in most areas.
Harvester
