Choke lever

My choke has also done this.
I took the plunger assembly off:
Peeled back the rubber boot which exposed the plastic housing that the shaft slides through.
The shaft has indented rings that the plastic grommet grabs onto.
There's a piece of thin (and strong) wire that is wrapped around the grommet which applies pressure to the shaft, mine was snapped.
I found some thin picture frame wire and re-wrapped the grommet, tightened with pliers, cut off the excess, slid the boot back down.
I hope this helps

Make a little v shaped wooden wedge to hold the plunger up to cold start. Pull it out an throw in your helmet bag to use next time. This will work until you get time to take the carb off and apart to fix the problem. Cheers John

Just run a zip ty around the outside of the choke lever at the top. It will pinch the little ridge inside of the choke boot that grips on the shaft. Problem solved.