Take the carb apart and clean it good, running it dry doesn't get rid of all the gas in the carb. Use Stabil and try to get gas without ethonal. Steve

+1 to ladylake suggestions.

The spinning chain indicates a higher than normal engine idle speed. This could be the result of the idle speed being set too high or a lean condition, with the lean condition I think being the worse of the two.

Lean can be caused by any number of things, a partially clogged carb, air leak, misadjusted carb, etc.

I hope you can find the problem.

Chain could be too loose if it spins at idle. I would remove the jets (note the number of turns) blow them out with carb. cleaner. If it will excellerate with choking it I would choke it and get the highest rpm out of it to run some gasmix through it and see if it clears up. If not I would try to adjust the high speed screw counter clockwise to richen up the mix and see if that helps.