looked up different ideas on you tube, you would not believe the crazy prices, for a simple device, one was $200 dollars. The home made ones, are interesting. i guy was using a rubber ring on the end of the throttle to act as friction, it worked. overnight
i was thinking about this, and came up with my own idea. go to a cycle shop, and ask for a scrap bicycle tube, 1/3/8 inch i found an old one in my shed. 24/1/38 inch. now cut it in half, and cut a piece off, 3/4 in. to 1 inch wide. use a square with the tube to get a nice 90 degree cut.
now stretch the tube over the end of your throttle. leaving a small overlap on the end cap, ie about 3/16 inch. this creates friction. Works perfectly. nothing to adjust with your finger for throttle position, easily shuts off, can,t jam. free and easy to do. i keep extra ones on my left handle bar to give to any motor cycle or moped rider i meet that wants to try it. easy to set on first cold starts to keep my bike running. Of course you need a a throttle that was designed with the end plate larger than your throttle grip for the rubber band to grip on,
i fitted another one on the inner end of my throttle grip, but not really necessary. i found. or if you want more grip, use another rubber ring over the first one you put on the end of your bar, this should double the grip. my bike is a jawa 210 economy 49cc and works great, but not legal in much of the world, so for safety when my M.o.T time comes up. i will temporally take it off. Hope you find it useful. paul.