Are the carbs fresh too? If so, how do you know the float height is right? With this much cranking you should have plenty of gas in the center carb if you pop out the sight plug you should be able to find some signs of gas. Also when pumping the throttle by hand, does the accelerator pump spray fuel? FWIW, I started my last fresh engine up with an electric fuel pump to avoid fuel supply issues on the first start-up.