Bad Starter?

I have a 1977 Johnson, 25Hp, electric start Mod#25E77S. Owned the outboard for about 4yrs & has almost always has starting issues. Turn the key & it would strain to turn over, then crank & start. Now it strains to turn over & won't turn over fast enough to start. Here is what I have done so far, checked the battery, good voltage 12.6V, connected jumper cables to the pick up battery while the truck is running, same result. Checked all wires & connections they look good. If I remove the spark plugs the starter spins the motor with no problem, it just won't take a load. Bad starter? Can this starter be rebuilt?
Thanks: John

Check for voltage drop at the starter. Check your voltage while cranking the motor over at the battery and then check the voltage at the starter while cranking the motor over. It should be close to the same. If not, your cables are bad or you have a bad connection on the cables between the battery and the starter. If it is very close to the same voltage then I would be looking at the starter.

Just to clarify the voltage drop test. When you hook the multi-meter up to the battery you want to connect the leads to the post on the battery and not the cable,terminals or anything that has a connection between it and the battery. Also when you hook up the leads on the starter, hook the the positive lead to the positive post on the starter and the negative lead to the starter housing if at all possible. The symptom you describe sounds like a loose connection. What happens is when you start cranking the starter over the cables and connections are cold. That causes high resistance which heats up cables/connections and when they expand from the the heat it causes them to get a better connection which actually helps the Amps get to the starter causing it to turn faster.

Thanks for the response, I'll give it a try.
John

KMixson said:

Check for voltage drop at the starter. Check your voltage while cranking the motor over at the battery and then check the voltage at the starter while cranking the motor over. It should be close to the same. If not, your cables are bad or you have a bad connection on the cables between the battery and the starter. If it is very close to the same voltage then I would be looking at the starter.

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Did the voltage test. While it was trying to crank had 11.9 at the battery, then 11.8 at the starter. Put in a new starter, and all is right in my world once again. Thanks for the help.
John