Stalling after warm-up mystery 5.0 Mercruiser Searay

[Exuma]

200 Series Searay 1994 with Mercruiser 5.0 Alpha 2 Gen 1. Two barrel.

I have a very odd issue that a few shops can't figure out that I need help with. We start the boat at the ramp, warm-up, and run for 30-40 mins around the lake with no issues. Then stop in a cove for 2-3 hours, then depart. That's when it will hesitate severely or even stall outright if you don't pull it back to idle quick enough. It will start right back up and idle all day long, no issues.

First try they found the auto choke was sticking and replaced that.

Second try they did replaced ignition module, ground wire, negative cable end, and negative batter(but a four barrel). A few members thought it was a engine compartment heating issue, auto siphon valve, fuel pump, or bad gas. The boat will run issue free for 30-40 mins, but after the start have issues. His final fix was changing the complete distributor and coil having heard these are a weak point on the 5.0.

It's in great shape but the big shops won't work on it anymore because of age, so tracking down myself or will try to find a small shop. $1K later, no fix.

 

[nola mike]

I'd grab a timing light and put it on one of the wires to rule out an electrical issue, make sure you're getting consistent spark. Double check that your choke is open and stays open. Have you looked at your fuel filter, make sure no water in there? Once it starts again, are you ever able to get it past idle?

 

[Lou C]

Have you actually verified that the auto choke is working as designed? Cold engine it should be close to closed; after a few min of run time it should be open or close to open. Some engines with carbs need the throttle cracked open a bit to start.

 

[Exuma]

I was thinking or replacing the fuel/water filter as they are easy and it's been more than two years since that's been replaced. Once we get moving I can look down the barrel and see all is open, but is that the only part of the choke on the two barrel? By looking at the timing/wires, is there a thought that once warm, the coil may be having issues? Once stalled, it will start right up and idle perfect. It's when we get moving that the issues start. I once ran for 45 mins from the ramp with no issues. Stopped for two hrs, then it had stalling issues every few moments (about every 5-10mins)

 

[Exuma]

I'd grab a timing light and put it on one of the wires to rule out an electrical issue, make sure you're getting consistent spark. Double check that your choke is open and stays open. Have you looked at your fuel filter, make sure no water in there? Once it starts again, are you ever able to get it past idle?

Yes, once it stalls, I can get it started and it idles fine. Then I throttle up and then it's a random stall or bad hesitation. The last shop did mention the choke was the issue then said they fixed it. It was sticking and caused a rich issue, stalling the boat. They also replaced the drain line from the carb back to pump.

 

[stresspoint]

i recon you have a fuel delivery issue , possibly a particle of some sort in the bottom of the carb that randomly blocks a main jet.
maybe an accelerator pump plunger bypassing.

just chucking this one out there . i once had a bad coil lead that had a broken carbon core act up only when restarting , however that would idle rough as , but may be worth a look .

 

[Exuma]

i recon you have a fuel delivery issue , possibly a particle of some sort in the bottom of the carb that randomly blocks a main jet.
maybe an accelerator pump plunger bypassing.

just chucking this one out there . i once had a bad coil lead that had a broken carbon core act up only when restarting , however that would idl rough as , but may be worth a look .

I was thinking fuel too, so before I replace with a $600 distributor, I may change the fuel pump, siphon valve, filter, and look at the fuel. How would one look at the accelerator pump?