Use a DVM and measure the voltage at these points while cranking;
battery
output of battery switch
started post

Use a load checker and check at above points not cranking and compare results. You can pinpoint starter, cables or switch.

Guys ,thanks for all the input,I'm definately going to check out your suggestions. I did buy a "marine" hi-output gear reduction starter,so that should help, and why I'm at it I'll put new cables in. This website RULES! THANKS

I assume you've read and clearly understand the rules here in the tech section as they relate to you sending each replying member with one case of beer,,,,,,whether we're right, wrong, or just cranking up our post numbers,,,,,,,,

correct me if I'm wrong....but I'm quite sure I saw different advance curves in the Mercruiser manual when I was gonna install my old stock big block thunderbolt ignitions in a friends small block boat when he was having some ignition problems. Mine are leftover from when I switched to the MSD's. Both boats are 1986 vintage with twins. You might want to have a friend at a good facility with all the factory books look that up for ya....but the curves are there and they are different.....

Put a vacuum guage on it and note how many inches of vacuum you are pulling at 10 degrees. Advance the distributor in small increments and watch your vac #`s You want your initial timing to be set at max vacuum at idle. Pick your ign module from there.

Dennis Moore's book on big block chevys has all the Thunderbolt IV modlules listed. My last naturally aspirated BBC really liked 18 degrees at idle. At the time I was running MSD's, they are mechanical so it is very easy to pick your own advance curve with the advance limiting bushings and springs. I do not run MSD anymore because they are too unreliable for me.

The V8-HP module only has 20 degrees of advance and a pretty short advance curve. It does not start to advance until 1500 rpm and is fully advanced at 3000. You could set your initial timing at 14 degrees at idle and by 3000 rpm you would be at 34 total. This might work real well for you.

Good luck,

Kurt

....sorry, I might have got a bit off track here. You starter is probably junk :D :D :D