If you have a spark and the engine won´t start then you 99% sure have no fuel in the cumbustion chamber. The remaining 1% could be due to lack of compression or a short circuit of the ignition loop after you have installed the plug. To make any engin start, I have found that pouring one shot glass of petrol into the air filter always works, if everything else is working. If it stops, try again and then if it stops, check the fuel flow, because it is 100% to be discontinued somewhere between the tank and the cylinders.