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Sparks, Zats, Ignition Coils, and Gas Mileage

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    Sparks, Zats, Ignition Coils, and Gas Mileage

    Evening Folks,
    I own a 1982 GS650GL, much thanks to the existence of this forum. Eventually I will get photos up. Disclaimer, little to no electrical has been done, cleaning connections was done. Here's the story:
    Not so much a problem, but a conundrum to think about. This past season I had problems with getting sporadic changes in fuel consumption despite having rebuilt the carburetor with new seals (including the fiddly little ones on 1 and 4 carburetor). I made sure to bench sync the unit using the guides by bwinger, and use a carbtune when I got it running to tune. I adjusted the four idles a bunch and my idle air knob. Yes I did replace the boot o-rings and checked for vacuum leaks (hot idle rpm creep). I got myself a gunson colortune, and despite my initial chinsy impression it did it's job. I was able to see the spark and fine tune the mixture.
    Here I am happily going along and tweaking the mixture, thinking maybe a spark isn't firing. Welp around cylinder 2 I see little to no spark and hear a crackling spark noise still. No the wire wasn't broken, but the spark plug boot resistor was, as I found out later. All that charge had no where to go except my hand when I went to adjust the plastic mirror on the colortune, thinking I misaligned it. Zat, and I sprung my hand off, shutting off the bike afterwards. There was no damaged chord, nothing frayed, spark plug had continuity even if it was worn down. It was
    about this time I started looking up replacement parts and right there in the spark plug boot listing was a resistance of 5k. Huh, I can check that and sure enough the spark plug was bad. I was concerned about the coils despite measuring 4.3 ohms and 33 ohms on the primary and secondary. Hence, I decided to buy RMstator brand coils as I had seen recommendations for their stators from this forum. Surely if they build a stator, they can build an ignition coil. They worked, welp the one didn't though nothing showed wrong with the resistance, no problem easy return. Between replacing the plugs, boots, and before replacing the coils my gas mileage shot up to 60 mpg from 45 mpg (multiple weeks). Great, eventually I got working new coils in, and replaced the olds coils (which I still have). Except now my gas mileage tanked back down to 45 mpg (similar routes of course). I did flip the parts in and out to verify, and everytime the mileage switched. It seems to be just the one that powers 2 and 3. All cylinders now have spark and fire, no more shocks to the poor hand Here is where I stopped for the season, as it was November. Too cold to troubleshoot the bike.
    Now that it's warm again and parts buying season is here, I am here trying figure out where to get an igniter module, the back up plan being go back to using the old working coils. With that
    story pending, any thoughts on places to buy from or other things to try? Also I think these coils are original with a tan color.


    Regards,
    Kemp​


    #2
    45mpg is about right. Sorry, it's hard to follow your post above. Too long. What is the problem?
    Ed

    To measure is to know.

    Mikuni O-ring Kits For Sale...https://www.thegsresources.com/_foru...ts#post1703182

    Top Newbie Mistakes thread...http://www.thegsresources.com/_forum...d.php?t=171846

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

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

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      #3
      Apologies about the length. I'll sum the problem up. After I replaced the spark plug boots/wires. I can get 60 MPG with my old coils, but the new coils drop it back down to 45 MPG. About 3 weeks of testing with both the old and new coils.

      Trying to figure out if the anyone has experience with new coils requiring more 12 volt current than the old igniter module can provide reliably. I will try and find the resistance sheet from measuring coil resistances.

      Comment


        #4
        The stock tan coils have primary resistance of about 4.2 ohms..their secondary resistance plug wire to plug wire (no boots) measures about 12000 ohms….add on a pair of 5k ohm boots , you get an overall resistance in 22k ohms. Stock plug boots were/ seemed higher at 10k ohms each on all the old ones that I could measure.
        Seems that 2 and 3 are behaving oddly with new coils….it’s possible that ignitor isn’t happy powering them .
        I still get about 55mpg with the original stock setup. These ignition coils appear indestructible….
        if you want a back up ignitor as insurance…let me know, as I have at least two spares….tested on my bike ten years ago.
        1981 gs650L

        "We are all born ignorant, but you have to work hard to stay stupid" Ben Franklin

        Comment


          #5
          That makes sense. Remeasured my old coils at 4 ohms primary (10.6mH Henry), and secondary of 12.2 kohm (42 Henry), and I will be measuring the new coils tomorrow with the warmer weather. Good to know that others are getting 55mpg with the stock setup. Your number lines up close to what I could measure on the old bad boots of 8k-9k ohms. Hrm, haven't quite haven't figured out how to check the ignitor. Getting an rmstator primary peak voltage adapter to add to the toolset though.

          I would definitely be interested in a spare ignitor, given my history with electronics on vehicles. Gotten better on knowing what to fix on the road. I will message you.

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