When it is running is the side that doesn't smoke feel cold? If so then it's not getting spark or fuel.A simple way to determine if it's getting fuel is pull the air filters or box if you have it and spray a few shots of starting fluid through the carb (throttle wide open) on that cylinder just to see if it fires and runs on that side.If it does than obviously that means your not getting fuel and you probably have a clogged main or a grain of sand stuck in the needle seat so it doesn't open...and yes it has happened to me.
Or swap plug wires and see if the side that doesn't fire switches.Check your grounds,harness plugs etc...just don't take it to a dealer to get ass raped for a simple fix...good luck