Under the carbs right side of the ski. But to jump the starter solonoid, it is in the rear black electrical box. Take a screw driver and touch the two large posts together. It will spark, and should engage the starter.
If your starter is pooched, you have to take the airbox off the carbs, then the flame arrestor bracket, and squeeze your way down there to undo the 3 6mm allan bolts and the two battery connections. If you dont mind buying two paper gaskets, remove the carbs, it will give you SO much more room. and less cuts. Those choke plates are SHARP. If you dont remove carbs, take a piece of 1/4 inch fuel line 2'' or so long and cut it lengthwise. Pull the choke and slide it onto the shaft. This should keep the choke pulled, it closes the bores so nothing falls into the carbs, and keeps you from slicing your forearms open. Been there, done that.