If the gasket is bad between the manifolds it will not cause a vacuum leak or hard starting. It will be an exhaust leak. Check the accelerator pump in the carb. Look down the throat of the carb with the engine off & open & close the throttle. Each time you open the throttle a squirt of gas should go in to the carb. throat. If that is working pump the gas pedal 3-5 times as you turn it with the starter when the engine is cold. These old carb engines don't work like the late fuel injection engines.
George
