Usually, with older engines that have sat forever, the carb is gummed up, but to verify that, use an eye dropper to drip some gas into the cylinder. If it starts, its a fuel problem.
You can pull the plug and hold it by the wire and ground it to the cylinder while you crank it. It should spark, if not you may have electrial issues. Another reason for no spark can be a bad ground. A sure fire way to test it is to have your friend/enemy hold the plug while you crank the motor. You will know real fast if its got spark or not. Sometimes the spark may look strong but when you put the plug into the cylinder it wont fire because it is too weak. 99% of the time though, if it sparks outside it will spark inside.
You may want to pull the air filters off and check them out eventually, since they could be heavily soiled.