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  1. M

    Mariner 8hp w Marathon only firing bottom spark plug

    Serial # 677-364773 My dad’s Mariner on the back of his sailboat always has run great. Started to lose power and just run on 1 cylinder. The top spark plug was always wet. He boat a new secondary coil(nice grey one, attached on the outside of the motor with wire going to spark plug). Put it on...
  2. M

    Mariner 8hp W8(M) w Marathon - no spark upper cylinder

    Just helping my dad with his outboard. Mariner 8hp on his sailboat. Ran rough, under powered. Pulled the plugs, top was always wet. We put a new coil pack(Primary ignition coil) on the top…the cylinder that wasn’t firing. He put it back on and same problem. What should I do now. Oh and what Ohm...
  3. M

    120 Mercruiser 2.5L - No spark

    Hi there. All of a sudden I have no spark. I had the carburetor professionally rebuilt. Hooked it all back up. Lots of gas, I have clear gas hose from the fuel pump up to the carb. Should start right up right, nope. Crank and crank and pump the throttle…Nothing! So I ground my test light and put...
  4. M

    Mercruiser 120 - water shoots out exhaust manifold wrong way

    I have a 2.5L Mercruiser 120. It would over heat if I run at speed, then I could slow down and it will cool down, so I idled at the dock, tested the flow coming from the transom, loads coming in. Then I took the hose that dumps water in the manifold from the thermostat housing and water would...
  5. M

    Temp rises while under way

    I have a 1970 Mercruiser 120 that running great now. It first ran hot a couple of weeks ago so I put a new thermostat in and no change(143 degrees). Then split the drive and put a new impeller and housing on. At idle at the dock everything is fine but then plane it off and get going the heat...
  6. M

    Timing a Mercruiser 120

    1970 2.5L. When I’m timing it with my light is each bar on the harmonic balancer = to 1 degree or 2. I need it 6 degrees BTDC. Do I go towards the arrow away from the 0 on the dial
  7. M

    Shift Interrupter Switch Merc 120

    Could someone show me the wiring diagram for a 1981 Mercruiser 120 that includes the Shift Interrupter switch that slows the engine down to come into neutral. Also would you have a wiring diagram for a 1970 Mercruiser 120 because I had to put a new(used) engine in. All the shift cables and...
  8. M

    Mercruiser 120 Shift Interrupter Switch

    I have a 1981 boat that had a seized 2.5L and I put a 1970 Mercruiser 120 in it 2.5. Boat runs great. There is just a little problem when I bring it into neutral it is a bit harder than normal, it stays in forward for a second but my gearshift is in neutral and then just goes into neutral. I...
  9. M

    Mercruiser 120 no spark

    Ready to put my boat in. Went over everything, put the gas to it, strong roll over but no start, the plugs are wet but no start. I changed the coil and still nothing. What new parts do I have to change on the distributor to get it sparking?
  10. M

    Transistor Voltage Regulator 1970

    My wiring diagram for my 1970 Mercruiser 120 says there is a Transistor Voltage Regulator. Is that on the engine? Or will it be mounted in the builge somewhere near the wiring harness for it?
  11. M

    Need wiring harness help

    i bought a 1981 boat that was purchased new in 1981. The deal was so good, something had to be wrong. It was. The engine had water in it and block is cracked. I bought a running 1970 Mercruiser 120 and dropped it in. Everything was great. Everything bolted up and I was almost in the water. Went...
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