I suck with chokes, but it is supposed to hold the valve closed when starting, then open slightly but still constrict the air while it warms up. As it warms up it should open more. It also controls the fast idle. When it is adjusted properly and operating properly, your motor should start right up cold and run decently until the motor is all the way warm. The trick is to get it to work properly. That might take some finesse to adjust it.