The choke mechanism also has what is known as a fast idle cam. When adjusted properly, it is the action of first opening the throttle. Pumping it a couple times will usually help prime the intake with fuel as well, since it creates a pool of fuel in the intake. This fuel pool helps in two ways; first it will lessen fuel condensation in the bottom of a cold intake manifold that can lead to a too-lean warmup (and stalling). Second, it boils off as the engine warms, also helping warmup. Gasoline engines don't mind so much being too rich, but they really don't run well being too lean. Anyway, now that you've opened and closed the throttle at least once, your fast idle cam (which is hooked to the choke mechanism) will swing into position under the idle adjustment screw, and will now hold the idle open higher than normal. Turn the key, and if all is adjusted correctly, the motor will turn the engine fast enough to start. While the engine warms up, the oil becomes thinner, the fuel vaporizes better, and the idle speed increases. Tap the throttle open again, and the choke mechanism will now pull the fast idle cam a little more out of the way, causing a lower fast idle. It won't happen unless you actually "blip" the throttle open, because the throttle return spring holds enough pressure on the fast idle cam that it won't move under the spring pressure from the choke mechanism. After several seconds, the choke mechanism will have started opening the choke butterfly further and further, until it's fully open well before you even see the temp gauge move from "cold". The choke butterfly moves without having to blip the throttle. After the engine reaches probably 100 degrees or so, depending on ambient temperature, a blip of the throttle will allow the fast idle cam to rotate fully towards normal hot idle. If you have a carburetor, it's cold, and a turn of the key will allow it to start on fast idle (remember: when you shut the engine down on it's prior run the fast idle cam was where it should be when hot) without first opening the throttle, then it is from a lack of maintenance, or you have magical leprechauns that come to your engine and set the fast idle cam during the night. As far as how often to pump the throttle, that depends on several factors such as humidity, fuel quality, ambient (engine room) temperature, engine design, engine age, etc.
Bottom line: If it works for your boat and the engine runs fine, then that's how it "likes" to be started.
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