I've got the same setup on my boat. You bring the throttle back until you feel resistance, that's idle. Then there is a spring that lets you push it another 3/8 of an inch to shut her down.
Here's some pics (before I cleaned and painted!). You adjust the idle speed with threaded portion and locknut. There is a spring that you cant quite see in either pic that allows you to push it further and shut it off.