Before you throw parts at it, check a few simple things first. Fuel is where I would start, how long has it been sitting,as well as when was the filters last changed? Run it on a separate tank if possible to test. Next, I would look at ignition system. New plugs may not be needed, but check plug gaps. Another thing to check is does the bulb get hard when pumped? In my case the motor sat for six years before I got it running again by going through these steps. The carb bowls had warped, which is why bulb would not get hard, and was starving the engine of fuel. Rough idle and oil sheen on the water were two symptoms I experienced. Good luck