Simply comparing the looks of the plugs might give some info.
If you haven't put new ones in for a while you might want to do that at least swapping in a set of "spares" you may have saved. I recommend using NGK only.
I think checking the valve clearances and compression might be the next logical step if new plugs doesn't help.
If you remove the valve cover, make sure to clean out any sludge in it especially in and around the crankcase breather baffle. Check the breather hose and make sure it's clear. If the outboard sits alot, critters build nests in places like that and I think excess crankcase pressure might cause a misfire condition like this.
the funny thing is it was running perfect in a barrel at home .sold it to a gentleman and he took it home put it on his boat and it started running this way.all within a day.I am at A loss he is bringing to me to have a look at.will swap the plugs and let you know.the fella I sold it to does not know how to change spark plugs LOL.