Since you have a gas engine just make sure not a lot of gas fumes are nearby when performing the spark test.
How old is the engine? How many hours? How good was the maintenance?
Step 1 -
fuel - Are you sure
fuel is leaving the carb into the engine. If you move the throttle does a little gas squirt out into the carb? If you can't take the throttle cable loose and open the throttle you will need someone to open the throttle for you while you look in the carb with a flashlight. You should hear and see a little squirt of
fuel. If you see a little
fuel squirt out skip the next step.
Step 2 - I bet it's
fuel related.
I would do this before checking the timing. To test this you could put some
fuel in the carb, just about a tablespoon full. Just drop it in the carb, put the spark arrestor back and try to crank. If it tries to crank just a little then your problem is in the carb. Stuck float or needle, maybe a bad accelerator
pump (part of the carb).
Step 3 - spark You already checked the spark at the plugs so that's not the problem. Could be a bad rotor (in the dist) or a bad dist cap. A crack (you probably wouldn't be able to see it) in the cap or rotor would cause problems. Could be the electronic module has gone bad. Did the LED come on before?
Step 4 - You can check the timing but unless the timing chain broke that's not going to be the problem. Engines don't usually die like that. Extremes would be a cracked crank or cam, but I bet it's not that either.