Define "It won't start" in the water. It doesn't crank over? Cranks but
doesn't start?

Here is my story of my 140 3.0L Mercruiser and its phobia of the lake:

Would start and run GREAT in the driveway with the hose and muffs on. Once
I get to the lake it would NOT start easily and run really rough until it
warmed up. I figured that a carb rebuild was in order as this is a 1977
engine. Carb wasn't it. Still wouldn't start nicely. Started getting
hydrolocking in the lake when trying to start. Decided to do some research
on the internet and discovered that the exhaust riser was prone to leaking
and allowing water to enter the exhaust ports. I pulled the riser and
filled the outside with water while watching the inside. It remained dry.
Pulled the head to see if it was cracked. Nope. Compression was a bit off
on #3/#4 but that was due to a tired head gasket. Pulled the exhaust riser
AGAIN and pulled all the cooling hoses going to the exhaust
manifold/waterjacket. I then carefully filled the waterjacket from the
front hose fitting with tap water and watched in horror as the exhaust side
started filling with water back by the riser. I had a cracked
manifold/waterjacket. I then pulled it and noticed a nice 7" crack running
the length of it underneath. I can only assume that it also cracked on the
inside between the water jacket and the exhaust paths.

This would allow me to run the boat in the driveway all day long. Shut
down/remove hose. Run to lake and have start very hard since the water from
"testing" it was slowly seeping into the last cylinder on my way to the
lake. I was able to remedy this twice while waiting for a new manifold. I
simply drained the waterjacket and block after running the engine. I still
drain the exhaust manifold after a day on the water "just in case". I hate
changing the oil. ugh.

So, check the exhaust riser, exhaust manifold, or head gasket. Is your oil
milky looking? Run the engine for a bit in the driveway and shut it down.
Grab a beer and wait a bit, then go pull all the sparkplugs and the coil and
crank it over. See if you get water shooting out of the last cylinder.

Nothing really major if you do the repairs youself. I dread car head
gaskets, but the marine engine is simple as it's cleaner and I can actually
get around it easily. I have seen the exhaust manifolds go for $350 (new)
to $150 (used) to $100 (new salvage).

Hope this helps.

-De

"Sean and Crystal" wrote in message
m...
Help anyone that might have a clue. I have a 1986 Invader with 140hp I/O
engine. Whenever I start it in the driveway, I have no problems at all.
When I am on the water, it doesn't want to start. Any suggestions would be
helpful. Thanks in advance.

--
SEAN