You should be able to get about 30 to 60 seconds or more of just idling. If you haven't leaned out the needles at all and it's running that hot then you have something causeing the engine to run lean. Something like a leaking fuel tank cap or a small hole int he fuel line, maybe the header gasket is leaking. I would check all that stuff out if you haven't leaned the engine out yet and it's still running rich.