Chuck has it well-covered. I usually don't bother with attempting to prime them. Chokes used to be a very common thing with four-strokes, where the choke was nothing more than a rubber cover that could be pressed against the carb inlet by holding a lever down. More recent designs don't necessarily have chokes like that. I usually remove them from my engines, as I don't use them. Four-strokes tend to be a little less fickle than two-strokes. They are more difficult to tune by ear than a two-stroke. Some people can do it, but I sure can't. I just use a tachometer, which costs about $20.