For the last few months my Yam 9.9 has misfired a bit for the first few
minutes of running, of course I made a mental note to investigate and never
did.

Today it didn't clear up as normal, infact it got worse and refused to run
at all in gear.

I pulled out a couple of plugs from the toolbox and put them in (while
drifting sideways down the river, lol) The old ones looked ok (90 hours) but
they came out very easily, they were almost 'loose'. The motor runs
perfectly with the new plugs, so was compression being lost past the plugs?
and how did they get so loose?