I have a 1989 Force 50 HP engine (507X9B) that starts and runs fine if I pull start it with a cord, but the starter is not strong enough to turn it over. If I take out one or both spark plugs, it will turn over OK. I have seen some past posts about voltage problems, etc. What should I lok for before I spend $150 on a new starter? Exactly how do I "jump" the starter to get full voltage to the starter to rule out a voltage drop in one of the connections?