Most starting problems are due to insufficient fuel. Dry plugs seem to confirm this. A good tickle is required. Hold the tickler down for 4 to 6 seconds on each side. Turn the engine over several times using the exhaust valve lifter to relieve compression. Nil or only a tiny amount of throttle opening. Try bump starting it in second gear (someone or two needed to push). If all fails suspect the magneto. Good luck - or break a leg as they say in the East End.