’67 80 HP, seems to starve out with throttle advance, plus rope start link

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  • July 2, 2020 at 10:49 pm #207517
    Alan
    Participant

      Hello to all;
      Yes, I still haven’t ironed all the bugs outta this motor. All but one bug, I think.

      It seems to starve out when the throttle’s advanced much more than half way. The rpm’s will continue to climb, but not a lot. Acceleration is steady and strong until then.
      And, when letting off the throttle, there’s a surge at about half way. The revs pick up a bit, and it surges forward a little. As the throttle is closing, at about half.

      Only gets up to about 4,200 RPM. In a flat bottomed aluminum runabout with two people in it.

      Tried 3 different props and maxed out the trim; no help.

      Otherwise it starts up the first time you hit the key, and the link to me rope starting it w/ ease is https://youtu.be/ehm0GoSSo0Q

      I’m starting to suspect a crack someplace or something.
      Here’s what’s been done.
      Carb’s been cleaned many times. like 10.
      Venturis centered with a centering tool.
      New gaskets, needles, and packings
      New high speed jets, correct size, installed with a jet tool.
      New fuel lines and clamps, from carb to tank.
      New fuel pump diaphragm, (twice now).
      New fuel hoses, CG compliant, new fuel fittings both ends. New pickle.
      Tanks cleaned, screens clear, new tank fittings, orings, etc.
      Tried two different tanks, and squeezing the pickle while Dad drove. No change.
      Full tune up, including all new spark wires.
      Checked linkage synch many times.
      OK, I’ll poke my head around it tomorrow, looking for cracks or leaks, muttering darkly. Anything else I can try?
      Many thanks;
      Alan

      July 2, 2020 at 11:30 pm #207518
      frankr
      Participant

        US Member

        I have to believe it is a belt timing or sync issue, but you’ve already denied that so I won’t argue. Still, it sounds like retarded timing. How about a sheared flywheel key?

        July 3, 2020 at 1:20 am #207520
        Alan
        Participant

          Many thanks Frank R;
          Agreed, this does sound like retarded timing, like it’s not advancing. I’ll check that thoroughly and try to look at it with fresh eyes.
          If it looks right I’ll post pics to confirm.
          Flywheel’s been off, twice, and key replaced. No concern noted. Also replaced the points cam, (right side up).
          All opinions welcome.
          Appreciated;
          Alan

          July 3, 2020 at 5:55 am #207524
          billw
          Participant

            US Member - 2 Years

            Sounds like you have flogged the fuel system pretty hard. However, the ultimate verification of your work would be to have somebody drive the boat while you take a pump oiler/ squirt can full of two stroke mix and shoot some down the throats of the carb, when the problem is occurring. If the speed picks up, you’d have a fuel issue. If it actually slows down, then your fuel system is probably okay. I am not exactly sure about the configuration of a ’67 80 but I seem to remember it has a belt driven mag, which rotates when advanced. Do you have a plug wire arcing out at full advance? Something like that?

            Long live American manufacturing!

            July 3, 2020 at 9:24 am #207527
            frankr
            Participant

              US Member

              It is a belt driven battery ignition distributor. I was patting myself on the back (wrong), thinking a sheared flywheel key, but I guess he has gone everywhere with it already.

              July 3, 2020 at 11:00 am #207532
              fleetwin
              Participant

                US Member - 2 Years

                The RPMs actually surge up/increase briefly when you are retarding the throttle? If so, just seems like something with the syncronization is off…

                July 3, 2020 at 1:08 pm #207537
                frankr
                Participant

                  US Member
                  fleetwin wrote:

                  The RPMs actually surge up/increase briefly when you are retarding the throttle? If so, just seems like something with the syncronization is off…

                  That is exactly why I suspected the timing is retarded. Spark must be at full advance before the carb butterflies kick full open or it will bog when they do open. Back the throttle off just a bit to “cruise” position, and the butterflies close down some and it takes off again.

                  feetwin and I are on the same page with our thinking.

                  Alan, you do have the breaker points set at 0.020″, don’t you.

                  • This reply was modified 3 years, 10 months ago by frankr.
                  July 3, 2020 at 9:33 pm #207582
                  Alan
                  Participant

                    All replies appreciated.
                    .
                    First two pics are with the distributor advanced by hand to the stop. They show the throttle position at full advance (not very far open) and the view of the control shaft in relation to the diamond shaped projection, (they look parallel to me).

                    The second two are of the belt timing marks.

                    The only way I’ve ever been able to set the points is to rope it around with a multimeter attached, and watch for them to open when the red marks on the distributor wheel line up with the pointers on the housing. The way it starts so easily and runs so smoothly at low and medium speeds, I’ll be surprised if the gap is way off.

                    But I bet this is one small mistake that I keep missing, and I am very open to correction or speculation.

                    I very much appreciate the support.
                    Happy Fourth of July to all!
                    Alan

                    • This reply was modified 3 years, 10 months ago by Alan.
                    July 3, 2020 at 10:25 pm #207594
                    frankr
                    Participant

                      US Member

                      Ok, you convinced me that I don’t know what’s wrong unless the flywheel key is sheared, and you assured me that it isn’t so I believe you. I realized that you know what you are doing when you said you used a venturi centering gauge. Not many people have one of those.

                      July 3, 2020 at 11:32 pm #207596
                      Alan
                      Participant

                        Many thanks for your support and prompt replies, frankr.

                        I’m not feeling like the sharpest knife in the drawer at the moment. The centering tool was loaned to me by parts guru Dan Gano. He’s been a great source for NOS parts. Lots and lots of NOS parts.

                        Sitting in the back of the boat at near full throttle, with the motor cover off, spraying fuel into the carb sounds sketchy when I say it out loud. But I see the wisdom and appreciate the suggestion. I would love to narrow down to either a spark or carb issue.

                        I sat in the back while Dad went from idle to top speed, repeatedly. I’ve pressed on the exhaust housing and didn’t see any transom flex or movement. Lund makes solid boats; I doubt it’s flexing. Hook, rocker, or whatever. The gearcase and driveshaft seem quiet and smooth, and there were no metal pieces on the magnetic plug when I changed the gear oil.

                        If anyone sees any issues with my synch or timing, I hope to hear those. Also love to hear any improbable or unlikely issues. Wrong part installed at some point? Upside down? Backwards?? A hairline crack someplace? Bizarre or improbable? Let’s hear it.

                        Thanks again, and very happy Fourth of July to all.
                        Alan

                        • This reply was modified 3 years, 10 months ago by Alan.
                        • This reply was modified 3 years, 10 months ago by Alan.
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