Drain the tank, drain the bowls of the carburetors, rinse the tank out with fresh gas, fill the tank with fresh gas, and change the oil. Remove the spark plugs and clean them. Turn the engine over several times before trying to start it, and do not rev it up really high at first. Check the tank for rust or corrosion, and the fuel lines for cracks. There may be varnish deposits in the carburetors, so run a premium grade of gasoline, preferably Chevron with Techroline, for at least the first four tanks. If there is rust in the tank, a kit can be purchased which has an acid for removing the rust, and an epoxy coating which is to cover the inside of the tank to prevent further rusting.