This thing:

I was feeling pretty good getting this thing humming like a sewing machine as it’s old as hell and gas and in a marine environment and did I mention old? 30hp Palmer gas engine from ~1970. Now it starts and runs and makes great power but once it’s hot it wants to shut down. Left idling it will turn itself off via a gradual loss in RPM or when hot and at higher RPM it’ll drop then cut out. Sometimes it’ll rise before it dies. It’s not 100% consistent which isn’t helping.

I don’t have a temp gauge but it doesn’t feel hot... But it has the feel of an overheating engine, the way it shuts down. It stumbles a bit if that makes sense.

I’ve opened the gas cap and it’s not vapor lock.

There’s a ton of cooling water going thru the engine and out the rear of the boat.

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Oil is full. Bit dark but plenty of it.

The gas in the tank is 1.5 years old. Water sinks so it’s not that as it wouldn’t run at all. I get a little puff of white smoke on startup but I’ve got a little bit of Marvel Mystery Oil in the fuel so that’s the likely cause. It goes away immediately after start.

Any ideas on where to troubleshoot this? Like, any? I'm at a loss.