Like Capt John says, check for spark first then do a compression check. I'm
still using the one I bought at K-Mart in 1963 for $1.97. Look at the
plugs when you take them out and keep them in order. There's a lot of
reasons why it may have gone to a rough idle and quit (but probably not
changing the impeller since last June is not one of them).
Some of the possibilities in addition to a bad power pack a broken rings,
scored cylinders, bad or blown out crank seals, one or more broken reeds,
bad electrics, timing off, etc.
I have an '88 200hp which I rebuilt 2 yrs ago. It had a hole burned in #6
piston w/zero comp and #1 cyl was scored. I found the bottom crank
bearing's retainer was broken, the balls were not spaced evenly, which would
have allowed the crank to wobble, sucking in air through the adjacent seal,
causing #8 to run very lean and burning a hole. Also, the guy I bought it
from handed me some "spare fuel lines" (1/8"ID x 1/4"OD). He said be sure
to ck them from time to time. (These are "bleed hoses) and they too, if
missing or broken will allow a cylinder to suck air and lean out).

"blair" wrote in message
oups.com...
I took my 1980 Merc 200 out this weekend and it just died. This was the
first trip of the year and I had a little old gas left in the tank. I
filled up with new gas, oil and fuel stabilizer. The engine ran great
the first night and then started running ruff in thr morning. It was
smoking more than usual at idle and then started sputtering and loosing
power at speed. My Tach went out first and then it just died. The
engine will turn over but it is tougher than usual with no positive
combustion. When I pulled the engine out of the water I had oil coming
out of the lower end.
I was lazy and have not replace the impeller sence last Jun.

I am not a great mechanic. Any recomendations on where to start? My
shop is backed up for over a month and I can't wait.
thanks