Well, I have had this problem happen to me twice now with my boat. It
is a 1978 Sea Star 165 hp I/O Mercruiser (Chevy Block?). It cranks
real slow but will fire if the battery is charged up. I took it out on
the lake it started up, ran it around a bit, anchored, did a little
fishing, wasn't getting any hits so I decided to move onto a different
spot. It would BARELY crank, no clicking, and actually the battery
would allow me to run the blower and such. So, after that, I had
someone tow me in. I bought a new battery (so now I have two). I took
it out yesterday, same problem, I hooked up the other battery while on
the lake and cranked it up and it started (BARELY). So I drove it to
the launch and shut it down to pull it up on the trailer, before I put
it on the trailer I thought that I would give it another shot. It
BARELY cranked again and wouldn't start. Hmmmm. I have a couple of
thoughts on it, but I don't want to go throwing parts at it when they
are needed. Any help would be appreciated though. I am thinking one
of three options he Starter, Alternator, or Voltage Regulator. I
did however notice that the battery cables were EXTREMELY hot on the
ground side and a little hot on the positive side. But, I did tighten
them up while I was out there so it wasn't a battery cable problem.
There is no corrosion on the cables whatsoever, so that shouldn't be a
problem. The starter is engaging, but this is what is puzzling me.

What are your thoughts?

smooth