Problems with my 1977 Mercury 150 outboard power of tower

[Bke12345]

Alright, iv got a headache of a project needing help with. I bought a boat and motor that doesn’t run. A 1977 Mercury 150 6 cylinder 2 stroke power of tower and I already put close to $800 into it so I guess there is backing out now lol. New stator, rectifier, New engine side harness and boat side harness, new starter, New starter Solenoid, rebuilt all three carburetors and rebuilt fuel pump. The CDi switch box that Is on the motor is no good so I have to replace that. I have new plug wires and plugs so yea I have done a lot so far. I have 2 questions. First question is sometimes when I try to start the motor by turning the key then I will try to turn the key off The starter will continue to turn and I have to disconnect the battery and I don’t know why. Second question is before doing so if anyone has a thought of what this can be, i’ve done a compression test on all six cylinders and I’m getting a reading of 65 on #1 - 35 on #2 - 90 on # 3 - 110 on # 4 - 115 on # 5 and 111 on # 6 Does anyone know if this could be a blown head gasket cause the first 3 are low compression or do I have a worse problem?

 

[Chris1956]

No head gasket on that motor. A likely overheat has damaged #1 and #2 cylinders. Not unusual at all, unfortunately. Pull the top transfer cover on the starboard side of the motor. You will be able to see the top 2 cylinders, pistons and rings. Look for scratches, melted pistons, aluminum on the cylinder wall etc.

Cylinders 3-6 are likely serviceable.

You kinda need to decide what to do next. For the motor to run properly, those cylinders need to be repaired. The powerhead needs to be removed, the crank and pistons need to be removed and the cylinders need to be rebored and new pistons and rings installed. If you can do the work yourself, it will cost $300-$400 dollars. If not, it will cost thousands, if you can find someone to do the work.

Your starter turning problem is likely bad wiring or ign switch. That motor should have a distributor. The rotor is not replaceable, and fragile. Be careful not to break it. The distributor caps last a very long time and are expensive to replace. Just clean the up. Make sure the carbon electrode in the cap is good.

The switchbox needs power on the red wire and the adjacent white wire to have spark. The red goes directly to the battery. The white wire voltage is fed from the ignition switch. Your starter and ign problem may be related to the ign switch or wiring..

 

[racerone]

Compression test is the first thing to do on an old motor before spending any coins !!----You have spent way too much already !!-------Remove the bypass covers on the starboard side to look at pistons and rings.---Sorry ---I think you are going to be disappointed .----Likely reach for a bottle of good stuff.----Your location ?

 

[Bke12345]

Kentucky

 

[Bke12345]

When I bought the boat it came with two identical motors so I might have a 50-50 shot here And the pistons, rings And everything inside the engine are OK because if so I can just swap

 

[Chris1956]

OK, do a compression test on the other motor and post it's result.