Don't over-choke the carb. Just pull and hold the choke rod for a second once the engine starts turning over. If you hold it longer than that, excess gas will runout of the air intake horn (back of the carb).
Marshall
If the engine has been run recently and is still warm, do not choke at all. Or on hot days do not choke. If the engine does not start without choking pull the choke for less than a second while the starter is turning over the engine.