1994 Johnson GT100 Purchase

[gatorfan6908]

Well, through my searches of Criagslist I have come across what I am hoping to be a great deal. This 1994 Johnson GT100 was listed for $350. Seller says it does run, only not below 1000 rpm. Also says that there is 120 compression on three cylinders with only 60 in the 4th. He first rebuild the carbs due to the idling issue because he figured the low speed jets were clogged. When that didn't fix the issue, he did a compression test and discovered the low compression.
I was able to talk him down to $250 for the motor. It comes with trim/tilt and all cabling and controls, only the controls are side mount and I have a center console, but that is for another forum.
Anyhow, I am looking for some insight to other things to look for with this motor and what else can cause the low compression. I plan on replacing all of the rings and honing the cylinders, installing new gaskets, etc... is this a good place to start? I know it is not a full fix, but with this restore I am doing on my boat, a full rebuild is not in the budget. You can check out the progress over at http://forums.iboats.com/showthread.php?t=570342.
He also said that it will need a new fuel pump, and said something about two types of fuel pumps. This one is a "special" one, no pun, that is what he said it is called.

Anyways, insight and info is appreciated!! Thanks!

 

[emdsapmgr]

Re: 1994 Johnson GT100 Purchase

You might be lucky that all it has is a blown head gasket. Pull the head off the side of the block that has low compression. Check the head gasket seal ring to see if it is intact or not. If it is intact, you'll probably be headed for a complete teardown and overhaul. Check the piston with low compression. Possible that it had a cracked/missing outer piston ring. It will be important to determine just why the powerhead failed. Was it lack of lubrication (dirt in the carb jets), overheating, misplaced water deflector, water in the cylinder, salt in the cooling passages, etc. You'll want to know why it failed so that it won't fail in that mode after the overhaul. If a ring let go, you may need a new head and piston. What type of fuel pump is currently on the engine?