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Think I've stuffed my ignition coils

Discussion in 'Technical and Troubleshooting Torque' started by klau, Oct 25, 2008.

  1. Being a newb, I thought it was a good idea to adjust the air/mixture screws on my 2 cyclinder bike individually (after cleaning the carbs).

    This was achieved by individually removing the plug cap from the spark plug, wrapping the cap in a towel, whilst I adjusted the other cyclinder (plug attached, bike running). All good until later when the bike wouldn't idle and sounded like crap. I had by then done the towel wrap multiple times per plug cap.

    Come next morning the bike won't start. Google around and it seems my mistake was not earthing the plug. With a sinking feeling, I did a proper spark test and there is only a weak yellow spark when it should be blue and strong...

    1st thought - stuffed the coils as stopped the coils from sparking and hence damaged them.
    2nd thought - what else might be damaged...

    Advice? Help!

  2. I assume you have taken the towel off?

    In the good old days, what you did was not too bad a way to synchronise carby tuning of twin cylender bikes. However some bikes with modern electronic ignitions don't like it.

    My bike comes with the specific warning that if you run the bike with an unearthed ignition lead (eg with a plug cap off) you are likely to stuff the diode board. I don't know what a diode board is as I don't surf or iron, but I know two things:
    1. My bike won't run without it; and
    2. They are f%@%king expense to replace.

    No doubt all bikes are different and so this is probably no help to you but I guess comes as warning to others to read the instructions first.

    Maybe if you said what type of bike someone who knows a little more about it could give more accurate advice.
  3. lol. Yes towel is off :)

    Bike is a yamaha srv250. I've done resistance tests on the coils (removed from bike), and wouldn't mind someone confirming whether the coils are definitely gone...

    From the workshop manual, both coils should be:

    primary resistance - 3.4 ~ 4.6 ohms
    secondary resistance - 10.4 ~ 15.6 Kohms

    1st coil
    Primary - 0-200 ohms multimeter setting gives 4.9 ohms
    secondary - 0-200 Kohms multimeter setting gives 23.4 Kohms

    2nd coil
    Primary - 0-200 ohms multimeter setting gives 4.5 ohms
    secondary - 0-200 Kohms multimeter setting gives 22.6 Kohms

  4. Running un-earthed coils shouldn't cause a major problem in the SHORT TERM. Those Yamaha ignition systems are quite robust.

    The resistances you've quoted are pretty close. BTW The coils need to be tested without the caps fitted.

    It's more than likely that you've simply carbon-fouled your plugs by running them without the leads attached.

    Try fitting some new plugs.
  5. Thanks MSCRacing.

    Did the resistance tests again tonight, less caps and also took into account the multimeter leads themselves, and the readings look to be in range now. Thanks for the heads up regarding the caps!

    Will get new plugs and update on how I go.

    Thanks again,
  6. Pull the plugs out and give them a brush with a wire brush, the put em in and see. Could save you the cost.