The job is fairly easy, but why do you need a starter? The charging system and battery should be fully working, low amps and volts will cause the starter to foul since as a series wound DC motor that is typically way over loaded, not enough energy supply will diminish the output of the starter. Poor electrical connections will also cause problems. You need to verify that the starter is at fault. Starter brushes may be worn down, the coils may be cracked in the fields, the armature may be open, or shorted. The connections may be bad. It takes a lot to kill these DC motors and all systems need to be up and running. So again why are you replacing the starter?