first thing i would do is pull off the fuel line at the carb inlet and crank the motor to check if fuel is actually getting to the carbs. i had a similar problem with my '72 145 and i found that the hose at the tank outlet had gotten old and saturated and actually collapsed where it bends and blocked fuel flow. also, i assume you'd have checked already, but is it possible that there is a plugged up fuel filter inline between the pump and the carbs?