solenoid tests- 1972 100hp evinrude

[bald tom]

I think I have isolated the starting problem on this oldie but goodie to the solenoid. The starter turns, but very slowly. below is the results of checking voltage at the solenoid input terminal (the heavy cable from the battery), the out put terminal (the heavy cable to the stater) and the starter it, with the key position off,on and start.

Ignition off on start
sol. in .00 12.9 3.8
sol. out 0.0 0.0 3.8
starter 0.0 0.0 3.8

Also, when I jump straight to the starter, it engages and turns quickly.

What other tests should I do to confirm it is the solenoid, or what other things should I test that would cause the very slow turn of the starter?

Thanks for your help!!