2007 Sea Ray 205 Sport with Mercruiser 5.0L MCM

Hey everyone, new to the forum. Found the forum via links from searches from the internet regarding a stalling 5.0L Mercruiser Alpha One.
I'm hoping to gain some feedback from folks here as they appear to be very helpful on all other topics!

I recently bought the Sea Ray from my father in law and he had mentioned that last time he had the boat in the water (Oct. 2017) the boat would "randomly stall, sometimes at idle".
After driving the boat to the house last week, I Yesterday, I took the boat out on the water, put it in the water and took off from the dock. While in the no wake zone, the boat stalled, right at the harbor entrance. When the boat stalls, the "alarm" sounded. After I turn the ignition off, wait a few seconds and restart the engines, she fired right back up again. Went out of the harbor at slow speeds and wanted to slowly take off. As soon as I went above "no-wake speed" (800-1000 rpm), the boat stalled again. Tried to re-start the boat, fired right up. This went on and on (starting/running/stalling) about every 20-30 seconds. At some point, it took a while longer to start it up, but then the boat finally ran and accelerated to about 2000-2500 rpm, ran there for a while and suddenly stalled again. This all went on for about 15 minutes, then she fired up and ran great for about and 1 hour of tubing with the kids and just driving around. When I turned off the engine, the motor cranked another 2-3 times, then shut off. After some swimming in the water, fired the boat back up again. It took a few tries again until I could put it into gear and not have the boat stall after 20-30 seconds. We stopped near the harbor to deflate the tube and when I turned off the engine, it continued to crank for about 10-15 seconds before it finally stalled. Finally, restarted the boat (it took about 10 seconds for it to fire up) and drove into the harbor and took the boat out with any further issues. Boat maneuvered perfect (forward/reverse) onto the trailer without any issues.
The last mystery was that the bilge drained for at least 2-3 minutes after I pulled the plug out. Not sure it was related, but seemed longer than I had noticed before.

If you're still reading...Thank you!
Based on some searches on forums I'm leaning towards inspecting the following: IAC (replace, incl new gasket?), spark plugs, inspect the fuel spray??? I'm honestly not quite sure where to start due to the intermittent performance of the boat. It almost seems like once it warmed up, it ran fine.

One final thought, when I cleaned the boat yesterday, I noticed some dark foam at the exhaust vents below the cushions. Cushions seem in perfect condition.

I'm new to marine engine repairs, but have worked one several motors in the past. I'm familiar enough to be dangerous but am at a loss here. Open to all input.
I attached a picture of the flame arrestor top with the motor serial information, etc.


Thanks in advance! Cheers!

First thought is fuel system contamination. Start by checking the fuel filter contents for anything but clean gas. Fuel filter is on lower front of engine on left hand side as u face the engine. Looks like an oil filter. Take it off and dump the contents into a clear jar or plastic bag. If there's water or debris likely you'll have to clean the carb and fuel system. Also can have a plugged fuel tank vent.

also there's no IAC on a carbed boat

re: "The last mystery was that the bilge drained for at least 2-3 minutes after I pulled the plug out. Not sure it was related, but seemed longer than I had noticed before."

Unless it rained and your bilge pump is inoperative, you should never get any significant water out. Just the amount of water that would remain in the bilge below the bilge pump switch automatic turn off point, or the point that the bilge pump will pull out below the inlet grate when running manually. I know this sounds gross, but dip your finger into the bilge water... if its salty ( assuming you run in sea water) you've got issues. Unless you have folks climbing into the boat soaking wet from in water activities all day, you should NEVER get back to the dock with more water in the bilge than when you left.

Hey guys, thanks for the quick replies. I will start with checking the fuel filter and go through the system to check for any blockages on the vent line. Sorry for being such a newbie.

As for the bilge, the more I think about it, it's most likely just from pulling the tube out, the wet kids and dogs. It's all fresh water (Columbia River, WA). I didn't run the bilge pump while out on the water, so I guess that would explain the larger volume. I'll be sure to turn the bilge on next time and check for good flow and level control.

One additional question...any feedback on the motor "cranking" after it was shut off? It definitely wasn't going at high RPM, but turned over a few more times.

Thanks again. Really appreciate your feedback!

Dieseling or run on. On a carbed engine you only turn off the spark to kill it. If you have carbon deposits or you are running lean and hot due to lack of fuel supply likely the combustion chamber is hot enough ignite the fuel still being pulled in from the carb and 'diesel' or run on.

Excellent. Thanks for getting me started. I'll report back with findings

Hey guys, finally had a chance to get some work done. I initially replaced the rotor and cap, as they didn't look very good. That didn't change much, to be honest. Then replaced the fuel filter. Added about 5 gallons of 100 octane fuel last weekend. Took the boat out, and after stalling two or three times, fired right up again and ran great for the three hours out on the water.
Back on the water today, topped the tank off with regular 87 octane fuel. Fired right up and ran great for an hour or so. When I turned off the engine to go swimming, it dieseled for a while, then turned off. From then on, it was a struggle to get back home.
It stalled quite a few times until I finally reved the engine for a while in neutral and then it finally ran well again and we made it back.
Will pull the fuel lines and see if I can lean out the carburetor.

Any other suggestions? Thanks in advance!! thanks

Run a can of decarb. through the engine, this will remove the excessive carbon on the pistons,follow instructions on can

No need to run 100 octane but if you can find 100% gas with no ethanol that would be helpful. This sure sounds like contaminated fuel. Top off the tank with good fuel and add the correct amount of Seafoam. Take the boat for a good long cruise and run the engine at operating temp for a while. If you still get these problems you might have to pump out the tank to remove the water or other contaminants.

Thanks guys, I'll try that for later in the week.

What did the fuel that came out if the fuel filter look like? Most likely need a carb rebuild and tgen check you're pumping good clean gas to it by disconnecting the fuel line at the carb, but thevfuel line into a container and crank the engine.

If you pull a spatk plug they probably look white and hot.