If the power valve is good it may be the wrong one or a vacuum leak is letting it open.

What is your idle vacuum and which power valve is in there?  The power valve
number should be half your idle vacuum reading.

No torn gaskets, clean carb gasket surfaces?

The fuel should come out the bowl sight plug and  also come out the bowl
overflow tube if the fuel pump is over riding the needle and seat.

 I'm betting it's the power valve though.

Be it the wrong one, a vacuum leaking allowing it to open early or what ever.

That just seems to be the area to focus on to me.

Good luck.

   I hope that doesn't mean water  IN  the ENGINE  too. 

If it's up the carb,  it sounds like way to little acc. pump.   Put on  50cc pumps and she'll pop no more 

That's a common problem with rebuilt starters from the cheap guys.   The armature has a  "dead spot"  but they don't catch it.

That sounds like the issue yours had.   It turns your starter into a roulette wheel.    When it stops there it won't start.    It may only land there once a month but....     

I'm an industrial electrician so I know how you feel with intermitant issues!  They are our worst nightmare   

I've been running 460 jets since 1977.  I agree with the other post, pressure test your logs.  They seem to be the weak link
in the water area. 

 If you had the bath tub intake gasket (hard to believe) that would be my second spot.

Third would be make sure your timing chain cover isn't eaten through somewhere and leaking in the crank case.   
I'm guessing the logs though. 

 If it were the timing chain it would probably lead to a lot of water.

Intake and logs can seep for quite a while.

When you say you changed the exhaust gasket you do mean the riser (round one) right?  If so were the flanges
clean and FLAT?

The other question is where was the boat last winter.....  you know where that's going.

Good luck, and remember to look for brown areas in the gaskets you took off.

Tap on the front fuel bowl.  The needle must be sticking.   If it starts with either and dumping some fuel down
the carb then you must not be pumping anything with the acc pump which = no fuel reaching the bowl.

You can have 14 pounds of fuel pressure but if the needle sticks.... she isn't doing anything.

Yea, what oil pan.  If you say 10 quart milodon marine pan.....      Been there
done that with the same results you're seeing now.
Just sayin   

Don't worry, no headers will go under the deck till they are water jacketed as the logs.
That's what I'm looking for...  Thanks again

If you don't ask you won't learn.   If there is anything new out there I hate to find out 5 years from now.
Thank you guys for your input.   I'll cut the ends for now.  I just may take the pony ride to lightning.
We'll have to do more measuring after it warms up a bit.   It's 2 degrees outside right now...
Thanks again.

Is anyone running headers under a sundeck?   Are there any reasonably priced water cooled headers
on the market?   I'm running long bolt logs right now.   It did have stock center riser manifolds but I had to change them out because they hit the tall valve covers.   
What are you running?

Gee, if it works out well you may create a whole new market for boat engines 
I think the torque will be it's down fall.  I hope not though, I'm rooting for you 

Just an update.   Nothing worked.  The stain is still there, it did fade a bit but far from good.
It was some sort of reaction to the tan rubber floormats I had over top of the ski deck to protect it
from the 2x4s that support the cover.

Check out armondos racing oil pans for boats.   I bought his 10 quart pan and pickup.  It fit great and I feel much safer than with the 6 quart