On Apr 3, 7:56 pm, Bruce in Bangkok wrote:
...there are zillions of Yanmar engines and I'd like
to know how to fix that problem.

Me, too!

I read a reference to one of your posts, quoted in part by Roger, that
sounded as though the RPM was only unstable at low RPM, I remember
something about 1,000 RPM.

No, it is generally stable at low to medium rpms (say ~850-1100). It
may hunt and/or loses power at higher rpms when loaded... Typically
it get progressively better as it gets warmer. I think everyone has
had a couple of swings at this and I'm not sure if there is much to be
gained by going over it all again. But I am listening. And, I will
be sure to report back if I fix it.

-- Tom.