You have to adjust the low speed needle. When was the last time you inspected your fuel tank and plumbing? Pressure check the tank? (Hold the carb line closed, blow hard into the vent line...pinch....wait 15 seconds....release the vent line and listen for a rush of air as the tank defaltes) Running strong for a couple of minutes then dying sounds a little like a lean condition. Is it really, really hot after it dies? Like...if you spit on the head does it sizzle off?? Cause it shouldn't. Is the clunk attached? Are all the gaskets in place? Is the carb fully seated against the crankcase utilizing the O-ring? Are all the parts on the carb gasketed and tight? Finally..is the carb clean?

And dude....the crank in that photo?? I wouldn't bat an eye!! That thing is fine. I'd be slapping that thing back together and running the hell out of it!! Make sure that your backplate gasket is intact, and that it is completely tight.