125 Mercury No parts low compression

Bowe

Cadet
Joined
Jan 24, 2016
Messages
22
Hello... hope I'm posting this in the right place.
I'm currently restoring an 18' 1968 Starcraft Starchief. Using the boat in the summer to fish our Colorado mountain lakes. Had a number of newer boats,
but recently bought this one as I just thought an old aluminum cuddy would make a nice classic fishing boat.
I believe the the 125 Mercury "tower of power" is original to the boat. The motor seems to start and run well. Spits water quickly and idles well. There is a bit of hesitation when you give it throttle, although this is all from the muffs and garden hose in the front yard and I did not rev it hard or for long periods of time. After it ran for about 15 minutes I did a compression test. All the cylinders are around 90 psi with #6 at 73 psi. I than did the old seam foam trick with a gallon of gas to de-carbon the motor and maybe fix a stuck ring in the low compression cylinder. Ran it almost 30 minutes off and on using the sea foam. Re-did compression test, same numbers.
So... here is my question. I'm finding there really isn't any parts for this old motor, so do I run it and hope for the best? Is 70 psi really that bad? Do I try to at least find a head gasket and reseal the head? Or should I just try and find another motor? I like the fact that the this motor is period correct to the boat, but I also want some level of reliability. I also have a 5 HP Mercury trolling motor and the lakes I will be on are not that big, so I think I could make it back.

I'm wondering what other would do?

Thanks.
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,616
It doesn't have a head gasket and the lower cylinder being 20psi lower is usually sign of lower seals being bad and water intrusion. It wont get water in cylinder on muffs. I would pull the intake transfer cover and see what the ring/piston look like. If really scuffed look for a used powerhead like a 115 and use the 125 wrap around.
 
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