Well, let's think about this:
1. You made a BIG mistake letting your buddy work on it. He obviously does not know what he is doing.
2. your horn honks when you pedal it. I would think that a lighting wire is cross connected to the horn wire. When you drop the engine you have to take apart the wiring junction to the left side above the petcock. I would start there. Make sure that the wires match up to where they are supposed to go.
3. I would think that your idling problem is in the induction system somewhere. Clean the carb again paying particular attention to the idle jet and passages. Double check the reed plate mounting. Check for air leaks.