DKW Motorcycle sparkplug bridging cause





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  1. #1
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    Jul 2012
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    Default DKW Motorcycle sparkplug bridging cause

    I've recently restorated a 1957 DKW Hummel, but picked up a problem with sparkplug bridging. It runs fine for about 20 minutes but then cuts out. When I remove the plug one can see small dirt/ gunk/metal bridge out the plug. When it is the removed the motor starts immediately. What can be the most likely cause - dirt coming from the tank via the carb or metal being picked up from the sump or other?
    2010 Prado 4.0 VX
    1984 Suzuki SJ410
    Conqueror Commander

  2. #2
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    I guess you are using unleaded fuel - if indeed the case it will thus not be lead deposits.
    It could be gunk coming from your exhaust blowing back into your combustion chamber. If you've not cleaned out the exhaust as yet I suggest you give it a good burn-out with a little fuel, fire and an air compressor. Very smokey, also bad for the environment but guaranteed to clean that baby up.

    In the mean time you may try running a slightly larger air gap on the spark plug.
    2011 VW Amarok BiTdi 4-Motion8)
    2006 Daihatsu Sirion
    6 x Water Buffalo's
    Honda Lawnmower

  3. #3
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    Thanks for the advise. I will give both a try this weekend. Must just be careful not to mess up the new chrome on the exhaust
    2010 Prado 4.0 VX
    1984 Suzuki SJ410
    Conqueror Commander

  4. #4
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    You say you restored it. Did you rebuild the engine too?
    If not, you'd better check your small and big end bearings. Worn and failing roller bearings can leave such small deposits on the spark plug.
    Secondly, it's a two stroke right? What two stroke oil are you using? Today's 2so is required in much less quantities than in the past and your engine was designed decades ago to run on a much thicker oil for proper lubrication.
    I would not imagine a large enough particle will get through a fuel filter and carburettor to foul a plug. If it is not trapped in the filter, it would most likely get stuck in a jet. Double check your air filter and airbox for dirt too. I also agree with decarboning of exhaust pipe. The worst it could be is a leaky head gasket. Those engines hated it and would melt a piston in seconds.
    I hope you get it sorted. It is hopefully just a silly little piece of dirt or something.

  5. #5
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    I remember getting this with an old 2 stroke Suzuki, it was caused by the brand of two stroke oil, switched to a different brand and the problem went away.
    '09 Suzuki Grand Vitara 3.2
    ''84 Bertone X1/9
    '80 Moto Morini 500

  6. #6
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    Thanks for all the advise. I've put an in-line fuel filter in, different spark plug (one with a sharp electrode), cleaned the filters, used different 2-stroke. Drove if for a while over the weekend and so far it seems to have solved the problem. Just to get new points because power is not 100%.
    2010 Prado 4.0 VX
    1984 Suzuki SJ410
    Conqueror Commander

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