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1975 Mako 20' - Easy-Off for bottom paint?

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  • 1975 Mako 20' - Easy-Off for bottom paint?

    I'm finally getting started on the 1975 20 project.

    The first order order of business is to see if the 1983 200hp Merc Black Max will run. I believe the last time it ran was in 2001.

    Last Sunday's list :

    swapped in a good battery,

    got the trim/tilt working (still need a new 20amp breaker and throttle switch; using a jumper wire to manually raise/lower for now)

    freed-up the steering cable/linkage (not great, but manageable)

    lubed all swivel and pivot points (again, not great but manageable)

    put in all new fuel lines-filter-separator-bulb

    1-1/2oz marvel oil in each of the cylinders and worked the flywheel slowly thru several revolutions (no binding or rough spots)

    re-built the fuel pump (first time, seemed pretty straight forward, hope I got it right)

    checked the carbs (clean as a whistle)

    installed new thermostats (looks like the previous mechanic clipped the old ones to let them run open all the time)

    installed a new impeller/seal kit (first time for me, little bit of a learning curve on this one)

    Click image for larger version

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    checked the spark plugs (all look ok) and did a compression check (127-123-127-129-125-124)

    Click image for larger version

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    Half way thru the compression check, the starter kept running after I'd turn the key off. I'm thinking either the solenoid went bad, or the key switch gave up. I ended up using the battery switch as the key to finish the last few cylinders.

    Hopefully, this Sat/Sun will be the day to run it. That is, IF I can get the solenoid/keyswitch resolved. The plan is to run it off a separate container of non-ethanol pre-mix instead of the orange goop in fuel tank.

    Any other suggestions on prep work before trying to start her up?
    Last edited by kgfisher; 01-19-2020, 11:30 AM.
    M20 project-Finally Splashed!

  • #2
    Did you actually rebuild the carbs or just inspect them? If they have been sitting for 13 years most likely there are little crystaline deposits all over the inside of the carbs that will block the jets or keep your floats from seating properly. I had a 1989 200 Blackmax that ran great as long as the carbs were perfectly clean.
    1977 Mako 23[br]Duxbury, MA[br]


    • #3
      when cleaning the carburetors is mentioned it's usually a reference to the float bowl and fuel jets, not the throttle body and venturi.

      if you have orange goo in your tank you can bet there is more of it in the float bowls. they probably look similar to the fuel pump.

      i would go ahead and replace the starter solenoid. if i had any money to bet that's where id put it...

      76 25 \"Aenigma\"[br]73 17[br]Richland/Long Beach, MS[br][br][br]17 project[br]


      • #4
        Yeah, a carb rebuild is probably in order. The fuel lines leading up to the fuel pump were full of the crystals you described. Beyond the fuel pump the lines, filter, and fittings were pretty clean.

        The starting problem resolved itself, probably temporarily, when I removed the solenoid to verify a part number. When I tested it, it checked out so I put it back on. That leads me to think it was the contacts sticking in the solenoid. New one will be waiting at O'Reilly auto parts tomorrow am.

        Is it common practice to "clip" thermostats like this to let them flow all the time?

        M20 project-Finally Splashed!


        • #5

          [i]Originally posted by kgfisher

          is it common practice to "clip" thermostats like this to let them flow all the time?

          this is usually a bandaid for some other problem
          76 25 \"Aenigma\"[br]73 17[br]Richland/Long Beach, MS[br][br][br]17 project[br]


          • #6


            The new solenoid turned out to be defective, so we put the old one back on to run it.

            Once all of the fogging oil and Marvel oil in the cylinders worked its way thru it smoothed out nicely.

            It had a very weak stream from the tell-tale until we removed the thermostats and ran it. I'm not sure what's going on with that. I don't think it got anywhere near hot enough for the t-stats to open.

            We ran it on a 20:1 pre-mix to make sure it had enough lubrication, and a very heavy dose of Quickclean.
            M20 project-Finally Splashed!


            • #7


              For what it's worth, I have a 1985 150hp Black Max that I have always run with the thermostats "cut" open. The manual would say not to do this, but I found that the motor does not flow otherwise (very weak stream). For me, it is not a huge issue as the water temp in Florida is always high so the motor does not suck up cold fluid.

              Boca Raton, FL[br]Current: 2002 253[br]Former: 1995 19[br]Former: 1979 19b


              • #8
                Hergro - Thanks for the comparison. Glad that is working well for you.

                Everything I've been able to find out indicates these engines don't put out much of a stream until the t-stats open. Until then, most of the flow comes out the two ports and the exhaust. All the videos I found online support that as well.

                I also read several comments by mechanics that caution against clipping them. The general idea is that the pistons are going to come up to temp regardless, and surrounding them with a "cool" block is a bad idea long term. When I combine that with the fact that I never had much faith (trust) in the Mercury mechanic my father used, I think I'll run with them in as designed.

                I also noticed that the meter shows 35 hours. I know he had a rebuilt power head put on at some point. I'm now wondering if maybe that really is all the time this one has on it. I'll look thru the paperwork to see if I can confirm that.
                M20 project-Finally Splashed!


                • #9
                  The next thing on the list is to pull the fuel tank.

                  Here are a couple of "Before" photos.

                  It made the first 1/2 of the trip from SoFla to NWGa on a flatbed we had some extra room on. Here's a shot of it being unloaded.

                  The 2nd part of the trip was a little more traditional.

                  A few pics after a good scrubbing, and then stripping the console, teak, fittings, rub rail, etc...

                  ... and what I drained out of the fuel tank...

                  M20 project-Finally Splashed!


                  • #10
                    After a morning hunt it was time to get the tank out.

                    As it turns out, removing the tank wasn't too bad at all. After all the horror stories posted on here I was ready with (4) 4x4's, (2) 6-ton bottle jacks, an old band saw blade and some chains, straps and cable. In the end, all it took was an 18" screw driver and some hedge trimmers.

                    The best news of the day is that the tank wasn't perforated at all. It's badly pitted and won't be re-used, but it held its own for almost 40 years. The aluminum fill line is a different matter. This corroded spot was directly under a seam in the small hatch in the coffin cover. I'm guessing that either the seam leaked, or one of the hatch screws leaked or maybe went thru the line and let the corrosion start. The rest of the aluminum line looks to be in good shape.

                    The last 1/2 gallon of 15 year old fuel. I've had Scotch that hasn't been aged that long.

                    M20 project-Finally Splashed!


                    • #11
                      The fuel fill and vent lines came out today. This was without a doubt the most aggravating part so far. The long straight run under the floor was pretty simple. Most of the time and aggravation was in digging out the foam around the elbows, and cutting the joints apart with a hacksaw blade. I was able to get it all out without cutting the floor, but I did cut out a section of the front corner seat to gain access for cutting the joints in the tubes.

                      I took a piece of 2" pvc and slid it over the end of the aluminum fuel line. I used a mallet to "tap" it all the way up to the elbow to separate the foam from the tube. Worked really well, just remember to 1> lay the pvc on the deck first and mark how far it needs to go in before you hit the elbow, and 2> Leave the pvc a foot or so long and drill a hole thru the end for a screwdriver so you can twist/pull the pvc back out periodically. There is a bulkhead you need to guide the pvc over just ahead of the tank tub front wall.

                      Next I cut an access hole in the seat big enough to reach in with a hacksaw blade to cut the joint apart. From there was just dig-cut-dig-cut.... The vent line was much simpler. A couple of twist and tugs and it came out.

                      Next items on the list are: 1>get a look at the stringers; 2>grind out the spider web cracks, screw holes, bow rail mounting holes, ...etc

                      And I was able to find an invoice for a rebuilt power head. It was done in 1992. Dad's health began failing in 2000, and the boat was mostly used on vacation in the Keys. Three trips in 7 years, probably 10-12 hours run time per trip. Sounds about right.
                      M20 project-Finally Splashed!


                      • #12
                        Look forward to following your project. Glad to see the old girl is gonna get some new life!


                        • #13
                          I'm onboard for this one too! [] Good luck!
                          1982 17\' Mitchell gone[br]1985 Mako 21 had 7 years[br]1951 15\' Critchfield first rebuild 1986 with a 35hp tiller gone [br]1992 17 Maverick rebuilt in 2000 still have[br]1973 Mako 20 currently rebuilding[br]South Florida, Don[br][br]


                          • #14
                            Stringers look good, although the pics didn't turn out too well.

                            Spent time this week after work seeing if the marinium items will clean up.

                            Here's a before and after...

                            M20 project-Finally Splashed!


                            • #15
                              Looks great! What did you use?
                              1982 17\' Mitchell gone[br]1985 Mako 21 had 7 years[br]1951 15\' Critchfield first rebuild 1986 with a 35hp tiller gone [br]1992 17 Maverick rebuilt in 2000 still have[br]1973 Mako 20 currently rebuilding[br]South Florida, Don[br][br]