How long should a coil last?

Forums Technical Two Stroke: Hints and Tips How long should a coil last?

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    • #8871
      A A A Dummy
      Member

      I had a break down last night and I think the coil has packed up. Road the big for half an hour and it cut out coming up to some traffic lights and would not start again. Pull it up onto the pavement and tried some more, no joy. I put a new plug in and it started. Got to the meet up fine. Bike started an hour later no problem. After about 10 minutes it was running a bit rough at low revs. Coming to a halt at traffic lights it cut out and would not start again. After half an hour checking fuel and spark I coy it running but vey rough and would not rev. Called the AA and after waiting an hour and a quarter I got it running again. I managed 5 or six miles before it cut out at a round about. Called the AA again and told them my new position. After another 40 minutes the AA man arrived. The bike had cooled again so I got it started and the AA man followed me the last 2 miles home.

      I have had these symptoms before when the coils is on the way out. When it gets hot it cuts out. You let it cool and eventually it will start again but will run for less time and cuts out at low revs. Eventually it will not start at all. If I am right and the coil has failed again it will be the 3rd coil in 10 years. How long do they last on average? Is there anything than can cause them to fail other than leaving them with the ignition on when its not running? The bike has an electronic regulator and is still running 6v.

    • #8873
      Derek Reynolds
      Participant

      Rarely had to replace a coil, in fact on bikes – never, though they can fail of course. 2cv coils are oil filled and can leak if cracked, and fail if ignition left on not running.

      Have you changed the condenser? Those little devils can give similar symptoms.

    • #8875
      A A A Dummy
      Member

      I am running an electronic regulator which means the condenser was removed when the electromechanical regulator was removed as stated in the fitting instructions. So I do not think it can be that.

    • #8878
      Derek Reynolds
      Participant

      Ah! Say – So you did. Not much help then. I take it the coil is of the appropriate resistance in Ohms.

    • #10955
      James Suttie
      Participant

      So you’re no longer using points?

    • #10963
      A A A Dummy
      Member

      I went through 3 coils in 2 years on my ts250 (completely standard 6v points, mechanical regulator etc).
      Started to cut out when warm, then wouldn’t start, got worse and worse. I changed everything and a new coil from mz-b sorted it. A few months later same problem and it caused me a lot of bother as I didn’t suspect the coil due to it being almost new. It threw me even more as I looked up the resistance measurements for it and they were all within specifications. It would even give a spark when the the plug was out and resting on the cylinder head but not spark at all when it was in the cylinder under compression and wet with fuel! Changed it as a last resort and no further problems so definitely the coil. The only thing that gave it away was a very slight amount of oil leaking from where the ht lead is fitted into it. I think I also cooked one by leaving the ignition on for a short while without starting it. So the new coil is this case lasted less time than the spark plug. My current coil is a used one off a ts150 project I am building and has lasted 8 months. I now carry a spare new coil and it is my first part I will replace if I have a problem. Most of the “magic” that is the spark is done by the coil, an early warning that your ignition system is starting to have problems is that the engine starts to miss fire when you put all the lights on, including brake light, but this can be your battery on the way out, if you know battery is good then it’s the coil.

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