Ongoing starting problem

Staring problems can be a plague. First determine if it's ignition, air/fuel or compression. I always do a compression test, pressure isn't the issue, it's the difference between the cylinders, more than 10 pounds you have a problem. Next try a careful and reasonable shot of starting fluid, just a shot while spinning the engine into the air cleaner. If it begins to start immediately, you're problem is carburetor or fuel supply related (which with today's poor quality gas I see it in 60 percent of my work. Never use gas with alcohol "oxygenated", and don't leave it more than 90 days without adding a stabilizer).
If it still shows no sign of life, pull your plugs and watch your spark. I prefer using an old spark plug with a wide gap like .040, clamped with a hose clamp to a battery charger clamp. Is the spark consistent, a nice blue arc? If so, one more somewhat common thing can happen. If your starter isn't in great shape it can pull too much amperage away from the ignition system. With plugs out does the engine spin freely and doesn't bind? Right after spinning the engine for about 30 seconds feel the large positive wire that runs to your starter (or your ground wire). Is it warm? If so perhaps your starter is in need of service.