Hi John,
The two most important things to make an internal combustion engine to fire is spark and fuel. If it fires with Startya Bastard means you have spark which leaves fuel or the lack of it. With your aircleaner off activate the throttle linkage while you are looking down the carby and watch if there is fuel getting sprayed on the butterflies. If no fuel, check if there is any in the tank. If there is fuel in the tank next step is to undo the fuel line past the fuel pump, point the hose into a container, get someone to crank the engine and see if there is fuel getting pumped from the line. Be careful not to have fuel sprayed all over the engine. If there is still no fuel then it could be faulty pump, blocked filter, blocked pick up in tank or crushed fuel line.
Let us know what you find.....