I don't know. I can't find any model specifics.
What would cause it? Lack of tension on the cable which would usually be found at the point where there is a screw, but it depends on what yours looks like. Usually on the bar, with a slide switch. You just need more tension on the slide.
If this px comes through ... you will see the screw in the middle. Yours may be a little different. Tightening that screw will put enough tension on the choke to stay out when you pull it out, but not too tight, as then you can't push it back in.
On the Harley's the cable pulls through a threaded plastic nut that has to be tightened down, but not so tight it breaks.