Sudden no idle, high idle or hunting idle is often a sign of an air leak.
Could also be a sign of dirt in the idle circuit of the carb. Previous posters alluded to this.
Plan of action?
1) build yourself a leak tester.
2) go buy a can of carb cleaner and a low pressure gauge (under 15psi or so) and the fittings to build a leak tester.
3) clean the engine in preparation to remove the carb and do a leak test.
4) do the leak test
5) disassemble the carb while it is off, remove the jets, clean all the passages with the straw that comes with the can of carb cleaner. Note the jet sizes.
6) check all the engine bolts with a torque wrench while you are in there and reassemble the pipe and carb.
7) check for operation, set the idle mixture and speed screw, they should function now.
8) not a bad time for a plug chop to verify jetting.
This will pretty much answer a lot of problems because while you are at it you will look at the reeds (thru the carb flange) and exhaust port and fix any small problems while you are at it.
This is about 2 hours work with a beer (after noon, coffee before noon) and the radio going.
You can avoid this simple check and diddle around with it for days, perhaps even selling it at a bargain price. Your choice.