Hi olly, glad to hear its not been laid up for the winter.
As Pete said, I also have a compression meter that you, or anyone else is welcome to borrow.
Anyway, some more 'Off the wall' ideas.
Was the engine once fitted with oil injection? If so the alarm may have sounded if something was up with the way it was disconnected, water ingress into a modified loom etc. I'm sure your engine should have once had oil injection, so maybe worth a look.
Have you by chance tilted the engine further than usual, there may well have been an old pool of oil laying in the bottom of the crankcase that found its way into the transfer ports.
My old 55 Suzuki had a bad smoking habit sometimes on start up, but only occasionaly after a longer trip to the slipway, such as when I towed it down to devon.
When the engine was left in the up position for quite some time the oil tank was much higher than normal compared to the pump, and I suppose a combination of the position in which the pump stopped and the extra head of pressure caused a leak-by through the pump into the inlet area behind the carbs so causing a lot of smoke on start up.
As its now run fine for a couple of hours I'd forget it and welcome your self to the worrysome world of boating. Was that a different rattle I heard?
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