First, lets get things straight. Some of the guys who have answered gave a good answer for lawn mowers and very small scooters, etc, but not motorcycles. Most carburatred bikes have a by-pass choking system, which is in reality a miniture carb in built into the side of the main carb. With the butterfly or slide closed, this miniture carb is turned on by the choke lever or ****, which pulls a plunger out, and clears the hole, which goes from the air inlet of the carb, to the body, between the butterfly/slide and engine. There is a tube which drops in to the fuel in the float bowl, this tube has a restriction, to form a jet, to control the flow of fuel on choke. This tube is blocked, when choke is closed. So, for the choke to work, the throttle must be closed, choke on, and start the engine. When started, give a bit more throttle, and as it warms up, slowly push the choke off (closed). This type choke has only been used for the past 40 years or so, on most all Japanese made machines, and a few others. Of course, the old English bikes had the Tickler on the Amal carbs, which allowed you to fill the carb float bowl, before kick starting. Harleys, unless you have an S&S Carb, and the mini stuff are the only bikes with the chokes you guys describe.