Choke

mine also does that. when you put it up it stays up but then when you kick the bike, the vibration causes the choke to go off.I just hold it up until it starts and then it will stay up.I dont know why it does it.

Just a guess, but maybe the choke assembly needs torn apart and clean out. It sounds like the detent ball is not coming out or staying out because it is either accompanied by a sagged out spring, or pre-mix is loaded in behind the ball in the spring??
Like I said, just a guess.
Stan

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 wrpped 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 then took my kids to Burger King with the $20 I was going to spend on a new choke plunger. :laugh: