My venerable (15yo?) 2T twin is auxiliary power for my even more venerable Hurley 22 sailer which is about 2 tonnes in cruising trim.

The engine has recently developed a pronounced intermittent vibration. The last couple of times it has started after half an hour or so and then stopped again after a similar period.

The start of the vibration has also been accompanied by an increase in revs though I suppose this could be the effect of the vibration on the throttle linkage. I've checked for rubbish around the prop each time but found nought.

It always starts and runs (apart from this) reliably.