1981 650GX Ignition timing

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  • G0FHM
    • Jan 2026
    #1

    1981 650GX Ignition timing

    Hi Guys,

    Can anyone tell me if the older GS is equipped to run on unleaded fuel?

    I only ask, as I have the motor split in two ready to take a new gearset, and when I dismantled it, I noticed that the mark the pickup plate was aligned with the mark on the casing, indicating 10deg BTDC as the manual says. But the manual makes no mention of 95 RON unleaded fuel (I know some countries had it long before we in the UK did, but I think it may have been a pipe dream still in 1981).

    On some older cars, the manual would advise retarding the timing by 5 degrees so that the engine would cope better with the lower octane (the first "unleaded capable" car I dropped 95 into pinked severely until I retarded it).

    Would this be advisable on the 650? The exhaust is fairly loud, so any pinking would likely not be heard unless it was severe, and in the limited time it has been on the road before tearing it apart again (130 miles) it has been running hotter than I think it should......

    Suggestions please?

    Thanks,

    J
    Tags: None
    • Nessism
      Forum LongTimer
      GSResource Superstar
      Past Site Supporter
      Super Site Supporter
      • Mar 2006
      • 35787
      • Torrance, CA
      #2
      The engine is designed to run on unleaded low octane fuel. If the engine knocks when hot, try "premium" fuel and see if that helps. If it continues to knock when using the expensive fuel, then consider retarding the timing. The timing itself is not adjustable as far as I know, but you could slot the timing plate a little I think. I'd consider this a last resort though.

      BTW, if the exhaust has been modified but the jetting is still stock that will make the engine run lean, which increases the likelihood of knocking. Some rejetting would be in order in this instance, not timing adjustment.
      Last edited by Nessism; 07-29-2014, 04:22 PM.
      Ed

      To measure is to know.

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      Carb rebuild tutorial...https://gsarchive.bwringer.com/mtsac...d_Tutorial.pdf

      KZ750E Rebuild Thread...http://www.thegsresources.com/_forum...0-Resurrection

        Comment

        • G0FHM
          #3
          Hi Ed,

          Thanks for that info!

          The pickup plate is slotted on ours, thus giving a few degrees movement either side of the line - Hence my asking.

          I'm convinced that the problems actually lie within the carbs... Just thought i'd ask while the thought was still in my head.

          Getting it running again is a way off yet.... Still waiting for shift forks and drum to arrive!

          Cheers,

          J

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