Vintage Mercury HP

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  • February 3, 2017 at 1:38 am #6256
    cheetahgod
    Participant

      I’m trying to figure out which vintage merc would work best on my 12ft class b utlity runabout.
      I’ve read the 10hp rated kg7 actually has a hp of 18-22hp
      What is the true HP of a kg7, Mark20, and Mark 25. How do these motors compare in performance and fuel economy.
      Thanks for all the help so far guys.

      February 3, 2017 at 3:33 am #52328
      jw-in-dixie
      Participant

        I have an eight-foot runabout and have run all of the motors you mentioned with pretty much equal performance. At 12 ft any of them would not over-power the boat. I think the KG7 is about 16 hp at the advertised rpm, more as the revs increase. Mk 20 and 25 would be about the same. I run a Merc 200 powerhead on a KE7 tower with a KG7 foot. Uses more fuel than the K models ’cause it has a larger carb. More like 22 hp, so I’ve read. Good luck, JW in Dixie

        February 3, 2017 at 3:52 am #52329
        Anonymous

          I have the KG7/Mk20/Mk25 as 19.8ci and the Merc 200 (and Mk28) as 22ci

          February 3, 2017 at 4:08 am #52330
          cheetahgod
          Participant

            I decided I’m going to put a kg7 on my boat.

            February 3, 2017 at 4:20 pm #52342
            chinewalker
            Participant

              US Member

              The KG7 and Mark 20 had nearly identical powerheads, so put out pretty much the same HP. The Mark 20 was rated at 16hp and that’s a pretty close approximation to the KG7. Mercury was careful to include an asterisk with their ratings with the notation that ‘horsepower varies with RPM’. That’s why they rated the KG7 at 4000 RPM, where it did, in fact, put out approximately 10hp. BUT, the little prop they shipped it with would allow RPM to peak well over 5000 RPM on many boats, where the motor was in full song. Around 5500 RPM, it might be putting out 16-18 hp.

              February 4, 2017 at 12:44 am #52353
              cheetahgod
              Participant

                what is difference between the KG7 and KH7?

                February 4, 2017 at 1:11 am #52354
                chuckw
                Participant

                  US Member

                  KG7 is a gravity feed carb, but Mark 20 has a fuel pump and a different carb. I have converted my Mark 20 to a fuel pump so I can use a single line tank. KG7 takes AJ32A, Mark 20 is AJ41A carb. KH7 is also a gravity fed carb. KH7s were last gravity fed before Mark 20 came out. KH7s were full gear shift and one year motors. Other than that KG7 and KH7 were basically the same.

                  February 4, 2017 at 1:32 am #52355
                  cheetahgod
                  Participant

                    So the kg7 has forward and neutral while the kH7 has reverse, neutral, and forward?

                    February 4, 2017 at 1:48 am #52357
                    westwind
                    Participant

                      Canada Member

                      No, the KG7 has no neutral, unless you include off being neutral. If it’s running the prop is turning. KH7 has full gear shift.

                      February 4, 2017 at 2:07 am #52358
                      cheetahgod
                      Participant

                        Why are the non-racing kg7 models more desirable than the KH7?

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