That really sucks about the shop, I wouldnt have charged you a dime for that service, I mean what did they do?, Nor would I have fucked with the carb. How could they think it needed to be leaner?
Has the timing been checked with a dial indicatior down the bore, or just on the flywheel?
Also, I know you said you have cleaned the tank and strainer, but have you checked the flow? Recently? I've had two engines that ran great, and woiuld putter out and die becuase they had enough flow to keep up with the engine at idle, but not at full throttle. Cleaned out they had lots of flow, but they sucked up some more shit quickly.
I'd clean her bore up and put some new crank seals in now. It would suck to have it back together, and go lean and kill it becuase of a crank seal.