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Rough Running A-65

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  • Rough Running A-65

    Just had an annual and everything looked fine. I't was signed off and I was a happy camper. Then the first time I was going to fly she was running rough and I had a 200 rpm drop on the left mag. Found both plugs black in #2 cyl. Cleaned them and moved them to another cyl. No Change. Compression test on that cly during annual was 76 over 80. Have new Slick mags with about 120 hrs. on them. Borrowed a lead tester today but haven't got to the airport yet. Any thoughts what I might check next ? Thnaks Marc

  • #2
    Re: Rough Running A-65

    The same exact thing happened to me once after an annual inspection. I found that I had smeared a small amount of oil/grease on the rubber part of the spark plug lead next to the spring that makes contact with the spark plug. This contamination was causing the spark to arc to the plug shield. I cleaned this very well and reinstalled; problem solved. Mabe you have something similar happening - it's worth a check.

    Allen,
    N27599

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    • #3
      Re: Rough Running A-65

      Was your timing fiddled with during the annual? On Slick magnetos check to see that the timing pin was inserted into the proper holes in the distributor block. If the magneto is pinned incorrectly the contact points can still be synchronized to the engine firing point, but the distributor finger is positioned over the wrong tower. This can lead to a confusing condition where the contact points seem to be synchronized, but the engine runs poorly on the subject magneto. (Courtesy Sacramento Sky Ranch, a highly recommended site).

      Ed@BTV VT
      TF 127

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      • #4
        Re: Handy link re: Small Continentals

        You may be aware of this site...I like to refer to it when I'm fooling with small Continentals. Dick
        Dick Smith N5207M TF#159

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        • #5
          Re: Rough Running A-65

          Checked the wire for grease and grime even used a lead tester on it today, still no luck. Took the leads off the left mag and moved them to the right and it moved the problem to the right mag. Could it be some sort of valve problem? Any other ideas ? marc

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          • #6
            Re: Rough Running A-65

            Originally posted by alwaysoar
            Was your timing fiddled with during the annual? On Slick magnetos check to see that the timing pin was inserted into the proper holes in the distributor block. If the magneto is pinned incorrectly the contact points can still be synchronized to the engine firing point, but the distributor finger is positioned over the wrong tower. This can lead to a confusing condition where the contact points seem to be synchronized, but the engine runs poorly on the subject magneto. (Courtesy Sacramento Sky Ranch, a highly recommended site).

            Ed@BTV VT
            TF 127
            Timing not touched. Took wires from left mag and moved to right this also moved the high rpm drop to the other mag. Getting desperat, any other ideas. thanks marc

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            • #7
              Re: Rough Running A-65

              Originally posted by Marc Reynolds
              Then the first time I was going to fly she was running rough and I had a 200 rpm drop on the left mag.

              Checked the wire for grease and grime even used a lead tester on it today, still no luck. Took the leads off the left mag and moved them to the right and it moved the problem to the right mag. Could it be some sort of valve problem? Any other ideas ? marc


              Hi Marc,

              I snipped two quotes from you (above) and I would conclude you had bad wire(s) on the left mag and now they are on the right mag.

              Is there something I overlooked?

              If not then why don't take one wire from the left mag (good wires) and swap it with one from the right(questionable wires)? When the bad mag switches back to the left mag then you know you just moved a bad wire and you can replace that one.

              Dave.

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              • #8
                Re: Rough Running A-65

                Something to think about the first start afer a anual inspection and you have a rough engine is "did someone drop a spark plug or plugs". That comes under the heading of SH.
                If it is on 1 mag from a cold start switch to the bad mag or if on both run for a short time on both then shut down. check to see if you have a cold exhaust pipe on a cylinder. That is the one not firing.
                Oh I forgot to say be careful. Use a temp stick or a birthday candle. A electronic temp probe would also be nice if one was at hand.
                Karl Rigdon TF#49

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