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Old 16 January 2008, 18:41   #1
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Short Circuited Plugs

Can anyone explain in technical words why do plugs short circuit when running under very slow speeds for long time uses, specially when throlling in 2 stroke engines ? Is there a way to avoid or minimize this plug problem ?
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Old 16 January 2008, 18:54   #2
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I hope this is what you are asking:

You need a spark.

The electricity only forms a spark when that is the easiest route for it to travel from the electrode to ground. If there is an easier route (e.g. via a damp/old HT lead, or the kill cord switch!) then you won't get a spark.

At low speeds the engine temperature is generally a bit lower. The fuel air mix is generally a bit richer. In a 2-stroke there might be too much oil. All that means you have more carbon atoms (from fuel and oil) which is being less effectively turned into CO2 (because of less oxygen and lower temperatures). The excess carbon can start to form soot.

Soot conducts electricity and as it builds up on the plug can provide an alternative path to ground for the electricity that should create the spark.
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Old 17 January 2008, 06:27   #3
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Spark plugs are self cleaning if used at the correct temperature. Half to full engine load for instance.
With lots of trolling , the combustion temps dont reach the tempereature to enable the plugs to self clean the carbon deposits.

You could lower the temp range of the plug.
Go for WOT blast every so often.
Change the plugs more regularly.

Or buy a fourstroke.

Not technical I know, It dosent need to be.
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Old 17 January 2008, 08:34   #4
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or troll on your Aux?
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Old 17 January 2008, 14:34   #5
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Quote:
Originally Posted by Rooster21 View Post
You could lower the temp range of the plug.
are you sure? I think you actually want a "hotter" plug. alternatively you can ajust the mixture - but there may be consequences for running at higher throttle/load if you do either of these
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Old 17 January 2008, 16:27   #6
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Iridium plugs are supposed to greatly reduce the chance of fouling.
take a look here for a cross reference and an explanation of why they work better.

http://www.spark-plugs.co.uk/pages/p...gk_iridium.htm
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Old 18 January 2008, 05:23   #7
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Plugs can sometimes fail suddenly. I had one go on the strimmer last weekend, had been roaring away at 3/4 throttle for ages (about 30 min non stop) and it just stopped dead. After a lot of messing around I eventually discovered that the plug was a dead short internally. It wasn't due to carbon buildup as it had been running flat out, I don't really know what suddenly killed it but a new plug fixed it.
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Old 18 January 2008, 05:45   #8
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Yep, I've had them fail too, especially in air cooled engines. But spark plugs do seem to get tired, even after a proper sand blast clean, truing the electrodes and gapping them they may not perform well. Dunno why.
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Old 18 January 2008, 07:56   #9
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Quote:
Originally Posted by Locozodiac View Post
Can anyone explain in technical words why do plugs short circuit when running under very slow speeds for long time uses, specially when throlling in 2 stroke engines ?
Here are a couple of links that may help you.

http://www.championsparkplugs.com/sp...Fouling&mfid=2

http://members.iinet.net.au/~pauldaw...park-plugs.PDF
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Old 18 January 2008, 09:20   #10
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Originally Posted by seahorse View Post
Thanks all for their respective feed back, although this is not my particular way of boating because I always boat near wot or cruising speeds, but this info might help other idler boaters to be aware of the problem.

Ribnet readers will appreciate to read how a theorically simple item can give you really unpredictable bad times. I usually recommend clients if excesive idle operation is done to wot their engines al least for 1 minute once in a while to help plugs clean themselves and avoid plug foulling and short circuits.

Bottom line : always cary with you a socket wrench and a spare plug for every cylinder your engine has whenever you go to sea or extra oars & crew and some beers just in case...

Happy Boating
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