"Billgran" wrote in message
. ..

"Chehalis Jeff" wrote in message
oups.com...

Remember,
always do compression tests with the throttle wide open.



Just for kicks, take a compression test on a two-stroke motor with the
throttle closed, throttle open, and your hand over the carb blocking off
all air flow. You will find that the compression numbers are all very
close. Why you ask? Because the exhaust port is open to ambient air until
the piston ring closes it off. On a two stroke, the compression only
builds when the exhaust port is closed off by the top ring. Try it, if you
don't believe.

Bill Grannis
service manager

Joe is right, compression is compression, ignition, and spark plugs are a
different issue.

If the engine does not show signs of discolored paint on the heads from
overheating, AND you want to mess with it, a 21 year old OB is not old if
taken care of, if it is corroded, filthy, signs of oil/gas leakage, bad
seals in lower, shifts funny, then let it go as parts. I have a 1985 Merc 4
cyl that is like brand new, compression 140 to 145 across all 4, you could
eat off the heads. Same as my 1989 15 HP Mariner. But I seen other OB's only
5 years old in 10 times more used condition than mine, from neglect, and not
having maintaining them. Watch out for discolored heads on any outboards!

If you are selling with a bad cyl, then let the buyer know he has an issue,
he may not mind doing it himself or getting it done if he likes the boat
and/or motor.

Mike