As Dell says, what aren't you telling us? Is the tractor running rough?Unless you see visible damage on the cap and/or rotor, they are not likely to be the problem. Don't discard them unless the motor runs better with the new ones; that way you will have spares! I have seen a tractor (two-cylinder Deere) run with the copper contact on the rotor broked off. The spark easily jumped the half-inch gap and the tractor had been running well. Embarrasingly, we had let the tractor run out of gas. After we added gas and she started right up, we put the old, broken rotor back in just for grins. She fired right up and pulled well. So, the problem is not likely to be the cap and rotor. They DO go bad; but not often. Instead, pay careful attention to the condition of the plugs. Surface rust means they haven't been changed in a while and may just have died of old age. But if you see a lot of oil on one of them, check the compression on that cylinder.
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