PCM Won't Turn Over fast enough to start

I have a 1992 Ski Nautique with a Ford PCM that I just bought this past summer. Since I got the boat it has always seemed like when trying to start it that the engine wouldn't turn over very fast. I'd use starter fluid to help and once it was running I'd keep it running. Since I know very little about engines I was hopiong for some insight. The boat has been sitting idle and I wanted to take it out, I cleaned the terminals and put the charger on the batetry and tried to fire it up, no luck this time. I had the battery tested and it was a little weak, but still good. Could this be the starter not turning over the engine fast enough? Thanks

 

Didja clean both ends of the battery cables? You may end up having to clean just about all the electrical connections in the starting circuit.
How about the other electric devices such as Nav lights, horn, bilge pump, ect. are they functional?

 

Does the motor actually not turn over fast with the starter or is it that the motor has to be turned over fast to start. I would suggest first take a compression test. If the compression is fairly even, should probably be at least 120# per cylinder. If the compression is low then the engine would have to be rebuilt. If the compression is ok then I would check the ignition system I don't know if this motor has electronic ignition or points. check or replace the plugs if it has points make sure the gap is correct and the timing is set right. If everything checks out then I would suspect a weak coil. An engine with low compression or weak spark will usually start with ether.

Dave T