Nitehawk,

I just recently had an engine that did the same thing. It wasn't an O.S. but a GMS. I did everything. I adjusted things slowly etc. I spent many tanks trying to get it to work. I finally gave up and sent the carb into GMS. Apparently they had put in the wrong idle needle. After they returned it, the engine ran great. It took me about 2 minutes to tune and I was flying. I was just relieved to know that I wasn't as big of an idiot as I thought. You may want to look into sending the carb in or trying another one on the engine.

Good luck!