If it's the original SU electric pump there are several things to try. They typically stop ticking once the float bowl is full. Since yours only ticks once you could have a blockage in the fuel line or the float valves may be stuck closed.
As a test, disconnect the fuel line at the carbs, aim it into a catch can and have an assistant turn the key to the run position. If fuel flows into the can and the pump ticks along normally, check the float valves. If you still only get one tick and no fuel flow, disconnect the fuel line from the pump's discharge port and repeat the test. (Be cautious when disconnecting the line as it (or the pump) may start pouring fuel by gravity). If you get fuel flow now, look for blockage in the fuel line to the front. If you do not get fuel flow and only get one tick, look for problems with the pump (burnt pump points, miss-adjusted toggle mechanism, etc).