Ahhhh, hard start and running rough

I bought my 1983 sn2001 last fall. It has the 351 commander.

Sunny Arizona gave us an early start on the season and we've had it out about 10 times. It has ran great, without any real issues. Occasionally, I would have to pump the throttle to get it to fire after sitting in the lake for a bit but that's about it. I had it out on Memorial day for 11 hours.

Today, I brought my kids to the lake. The boat fires up and runs great from 10 am til 4:30.

While pulling my oldest son on the kneeboard the boat lost power and started to sputter and vibrate. I shut it down immediately. Upon restart the boat will fire but quickly dies. I was able to get it to run eventually and running back to the loading ramp the boat has seriously decreased power, won't pull over 3k rpm and it kind of sounds like a car with a hole in the exhaust.

The boat did not overheat. In fact, since I cleaned out the strainer and put a new impeller I've never seen the temp over 110.

My plan is to replace the plugs/wires and hope I'm missing on a cylinder or a few. I bought autolite 24s earlier this week but haven't put them in yet.

I guess I'm asking if I should be looking at anything else?

Thanks in advance.

You may want to check your distributor cap for any moisture. I had similar effects and just needed the distributed to dry out. See if anything is spraying within the engine compartment. Good luck

Also, its definitely running rich.

I'll do a compression test tomorrow morning and post the numbers. To me, water in the cylinder means blown head gasket or cracked block. After doing the compression test, I'm going to pull the heads unless someone says otherwise.

Thanks

+1 what Tim says. He walked me thru the manifold thing on the Shamrock. Pulled the manifold on the side that water was in - you could actually see the rust track the water left in the manifolds exhaust port

I bought the boat last fall (october) The first time I took it out it was overheating, It never got hotter than 190. I cleaned the strainer and it has ran 110 ever since. It possible, maybe even likely that the previous owner overheated the boat. I have had it out 8 times without issue (until yesterday) since I cleaned the strainer.

you're going to need new intake gaskets when you re-assemble.   pull those gaskets off and clean everything up.   leaking intake manifold doesn't explain your loss of compression though, that is a function of the valves/rings. Do you have a leak down tester by any chance?   If not, they can be had at harbor freight pretty cheaply.    A leak down tester will show the source of the problem, and what your next step is.   

Thanks for the input so far. I'm having a hard time figuring out how this issue could suddenly manifest after 50 hrs of great use without overheating or anything. When it started to run rough, the temp was 110, I could put my hand on the block, exhaust... I'm going to check on suspected crack area. I've pulled the exhaust and banks 1-4 had water in them, but that was expected with all the water in 1 and 2. The other side was dry.

What should I be looking for on the exhaust manifolds for failure or a water issue there?

Should I pull the heads or wait for some more input?

Kens right, not (just) an intake or exh manifold issue with those compression results. I'd still be looking for intake or exhaust manifold damage as you disassemble... but that head has to come off at a minimum. Same goes for the exh manifold on the other side (sounds like both banks had water in the cylinders).

I'm hoping this means I beat the odds and fall into the 5%. It definitely looks like the head gasket between 1 and 2 is gone. What do you guys thing?

Replace the gaskets, reassemble and hope for the best?

Try to locate some gt40p heads and replace the heads while I've got everything disassembled?

Any other options or considerations I need to look into?

Look at the yard sale post in the for sale section... Jody may be able to hook you up on the top end pieces... I saw a head, and intake/carb etc... might be your lucky day

Besides the reasons mentioned for head gaskets leaking, they can just plain get old and wear out too, so who knows what happened before you bought the boat.

It may have just been the end of the road for the original gaskets.

By the way, I'm gonna get a few lottery tickets for myself

PS A leakdown test in this case would have told you nothing

You might need some parts from this