I think would be to make sure you're getting fire to the plugs, and that the plugs aren't corroded.. as well as the distributor/rotor,if you have one.. Could even be plug wires.. Then you gotta get the fuel pump..
Fuel will go bad, over time.. in fact, fuel will turn into a molasses looking glob over a few years..
When you're turning it over - can you have someone spray carb cleaner or another ignition substance into the throat of the carb? Prime it, in other words.. That would probably be the first thing I'd try as its the easiest.. If it briefly fires up, you know its a fuel/carb issue..
Regarding the distributor/rotor, I've taken a piece of sandpaper and lightly sanded the rotor and distributor contacts to make sure they aren't corroded and have nice clean contact points..
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