Possible diagnosis and is there a simple remedy?

[novice boater54]

I've acquired a 1975 150HP (1500) Mercury outboard which I've found to have low compression on two cylinders, spefically #'s 1 & 3. Readings of minimum 30lbs or less (as my gauge only goes as alow as 30lbs).
I'm trying to determine some inexpensive alternatives with out having to tear down this beast of a motor to get a more deatiled diagnosis and contemplate a repair procedure.
The other cyl's 2,4,5 have over 120lbs and #5 was inacessible due to lack of adapter but appears to have significant compression realted to the low two cylinders.
Any suggestions?
I wish I had (if there's a tool such as this available), an inexpensive fibre optics tool wich could peer into the cylinder hole from the spark plug hole and at least indicate whether the piston/s have holes in them or not and or the preliminary condition of the cylinder wall.
I'm more leaing towards stuck rings as there's no indication of overtheating such as scorched paint etc.
this motor apparently had been sitting for a couple of years and ran prior to that, so I'm told.
Also can someone tell me where to find the thermostat on this motor?

 

[Droll]

Re: Possible diagnosis and is there a simple remedy?

You could remove the transfer port covers on the starboard side of the block, this will give you access in to the pistons tru the intake ports.

All tree covers removed in this picture ( it's a 1984 115hp )..

Don't know what you will find but...

• #1 are the first to go if there's a cooling problem
• #3 are the fist to got if the engine was running to big a prop ( NOT reaching 5800 at WOT are a inline 6 killer... )

Parts are no problems on this engine, can get it up and running in a couple of days


Arne Kjetil