1975 Merc 650 running issues

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  • September 14, 2019 at 7:37 pm #183353
    shoestringmariner
    Participant

      I ran my motor a fair bit this week. Runs well to great most of the time. Startup is a bit rough (low throttle response, lean sneezing, sudden dead stops, generally rough running) once warm it usually runs pretty good. This week, the top end power felt off. It would run strong, then 95 or 90% then 100% and repeat erratically. Fresh gas, Amsoil syn oil mix. Fuel stabilization and a glug of sea foam. new tank all new lines. I did not touch carbs or fuel pump this year. Ran flawlessly late last year.

      Plugs look good good and consistent.

      the only thing I found is the timing belt looks sloppy. I get 1/2” deflection in belt tension, maybe more. What’s the norm?

      I sense this is an electrical/timing issue. Could this be a trigger issue?

      I hope to use this all next weekend but it’s semi-remote water and I’m not confident

      September 15, 2019 at 6:40 am #183367
      billw
      Participant

        US Member - 2 Years

        See if you have moisture in the distributor cap. Certain atmospheric conditions can make that happen. I remember that used to happen sometimes, when those distributor engines were more popular.

        Long live American manufacturing!

        September 15, 2019 at 7:38 am #183368
        shoestringmariner
        Participant
          billw wrote:

          See if you have moisture in the distributor cap. Certain atmospheric conditions can make that happen. I remember that used to happen sometimes, when those distributor engines were more popular.

          Excellent, thank you. Maybe that’s it, It’s been cold, windy and rainy here.
          I used to hear people say to spray wd40 on wires and caps in wet weather on old type systems (flatheads, magneto drives etc)…truth or fiction?

          Is the soft belt tension anything to worry about?

          September 15, 2019 at 9:15 am #183376
          mercuryspecialist
          Participant

            I agree that checking/cleaning the distributor cap is excellent advice. Possibly a new distributor cap carbon brush & spring might be a good idea also. I cannot see the application of WD40 on a upside-down mounted distributor cap to be helpful.
            Carburetor float levels and a stretched fuel pump diaphragm would be two other causes.
            The timing belt is not adjustable for tension, and ½ inch does seem a little high, so a new belt may be needed. If it is the original timing belt, it is due. The two sealed ball bearings (which support the rotor shaft) should be considered also (if original), or a new belt will typically break when a bearing(s) binds.

            Regards,
            Joe
            (770) 597-5992

            September 15, 2019 at 10:09 am #183381
            shoestringmariner
            Participant
              mercuryspecialist wrote:

              I agree that checking/cleaning the distributor cap is excellent advice. Possibly a new distributor cap carbon brush & spring might be a good idea also. I cannot see the application of WD40 on a upside-down mounted distributor cap to be helpful.

              Carburetor float levels and a stretched fuel pump diaphragm would be two other causes.

              The timing belt is not adjustable for tension, and ½ inch does seem a little high, so a new belt may be needed. If it is the original timing belt, it is due. The two sealed ball bearings (which support the rotor shaft) should be considered also (if original), or a new belt will typically break when a bearing(s) binds.

              Regards,

              Joe

              (770) 597-5992

              Excellent, thanks so much. I doubt it is original as it looks petty good. I’ll change it this winter to be sure. Appreciate the tip on the bearings.
              For this week, I think I’ll leave it be and let it dry out in the garage so I doint mess it up and ruin the weekends plans. The plug wires are old. I’m afraid to disturb them too much.

              September 15, 2019 at 10:56 am #183385
              The Boat House
              Participant

                September 18, 2019 at 11:02 am #183590
                John Schubert
                Participant

                  Lifetime Member

                  When we used that type CD ignition with the plate with timing slots on our Quincy Loopers,the disc acted as a pump & inducted moisture resulting in erractic firing. (missing). The fix from Quincy was to drill a 1/8″ hole in the bottom of the distributor cap. I attempted to race my 4 cylinder C that Quincy build 3 times with the ignition mis-firing & never knew what the issue was. It was our first time using that ignition. While testing at the Nationals it happened again. Took my distributor cap to the Quincy trailer & was promptly told about the fix by them & Gerry Waldman. Geez, why didn’t Quincy do it prior to shipping to me. The fix worked & I finished 4th in the championship ahead of the Quincy entry.

                  September 22, 2019 at 7:13 pm #183905
                  shoestringmariner
                  Participant
                    The Boat House wrote:

                    Excellent I will look for that

                    Thanks

                    September 23, 2019 at 6:44 pm #183953
                    shoestringmariner
                    Participant
                      John Schubert wrote:

                      When we used that type CD ignition with the plate with timing slots on our Quincy Loopers,the disc acted as a pump & inducted moisture resulting in erractic firing. (missing). The fix from Quincy was to drill a 1/8″ hole in the bottom of the distributor cap. I attempted to race my 4 cylinder C that Quincy build 3 times with the ignition mis-firing & never knew what the issue was. It was our first time using that ignition. While testing at the Nationals it happened again. Took my distributor cap to the Quincy trailer & was promptly told about the fix by them & Gerry Waldman. Geez, why didn’t Quincy do it prior to shipping to me. The fix worked & I finished 4th in the championship ahead of the Quincy entry.

                      That is a very cool tip, thank you

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