1972 Mercury 20 hp

Home › Forum › Ask A Member › 1972 Mercury 20 hp

Viewing 10 posts - 1 through 10 (of 21 total)
1 2 3
  • Author
    Posts
  • August 16, 2021 at 9:22 pm #245005
    farmboy71
    Participant

      1972 Mercury 20 hp. I got it on trade. It has 120 lbs of compression in both cylinders. I put new plugs in and I have good spark. It will only pop when I try to start it. Any ideas on where to begin.?

      August 16, 2021 at 10:46 pm #245008
      wedgie
      Participant

        Fuel system.

        August 17, 2021 at 5:37 am #245011
        billw
        Participant

          US Member

          On that engine it should be obvious which spark plug wire goes on which plug, so I doubt they are reversed, unless somebody moved the wires from one coil to another. Using a pump oil can or a syringe, squirt a small amount of fresh gas/oil mix directly into the throat of the carb and try to start it. If it fires with more life and even runs for a few seconds, then you’ll need to clean the fuel system out, especially the carb.

          Long live American manufacturing!

          August 17, 2021 at 8:07 am #245015
          farmboy71
          Participant

            I gave it a shot of starting fluid and it still only pops. I also tried changing the plug wires to make sure. I got a really good backfire then.

            August 17, 2021 at 3:40 pm #245031
            Rusted Junk
            Participant

              Starting fluid is not a good choice for starting an old outboard, not any lubricant in that stuff, fuel /oil mix better for the old motor.

              • This reply was modified 3 years, 8 months ago by Rusted Junk.
              August 17, 2021 at 5:42 pm #245035
              farmboy71
              Participant

                I am aware of that, I use it sparingly. I have taken the carb apart twice and blown it out. I know fuel is making it to the carb but unsure if it is being pulled into the motor. Still will only pop.

                August 17, 2021 at 5:51 pm #245037
                dave-bernard
                Participant

                  US Member

                  clogged exhaust ports ???????

                  August 17, 2021 at 6:26 pm #245038
                  billw
                  Participant

                    US Member

                    Well it would be pretty dang hard to do on a 20 Merc but sheared flywheel key? Bring #1 cylinder to TDC and see it the TDC mark on the flywheel lines up with what I recall is a pointer?

                    Long live American manufacturing!

                    August 17, 2021 at 7:53 pm #245041
                    farmboy71
                    Participant

                      Would I need to take the side plate off to check the exhaust ports?

                      August 17, 2021 at 7:55 pm #245042
                      farmboy71
                      Participant

                        I have had the flywheel off so it is not the key. I read on a forum that it could be the top crankshaft seal. Is that possible?

                      • Author
                        Posts
                      Viewing 10 posts - 1 through 10 (of 21 total)
                      1 2 3
                      • You must be logged in to reply to this topic.