Short Circuited Plugs

[Locozodiac]

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 ?

[Poly]

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.

[Rooster21]

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.

[9D280]

or troll on your Aux?

[Poly]

Originally Posted by Rooster21

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

[ian parkes]

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

[BogMonster]

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.

[jwalker]

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.

[seahorse]

Originally Posted by Locozodiac

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

[Locozodiac]

Originally Posted by seahorse

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

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

[ian parkes]

Originally Posted by jwalker

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.

Don't ever sandblast plugs or even use a wire brush on most modern plugs . Only solvent should be used .

[jwalker]

Originally Posted by ian parkes

Don't ever sandblast plugs ..

Why?

[ian parkes]

sandblasting can force tiny particles of sand betwen the electrode and the insulator and into the body of the plug . When it gets hot the sand expands and cracks the insulator or causes hot spots which lead to plug failure .

The fine elecrtodes of modern platinum plugs etc are easily damaged even by wire brushing

[Locozodiac]

Originally Posted by ian parkes

Don't ever sandblast plugs or even use a wire brush on most modern plugs . Only solvent should be used .

Ian, what solvent do you use or recommnd for cleaning.

Have benn cleaning plugs with Acrylic Thinner for years with excellent results. Dip/soke the plug electrode and all thread height for 30 secs in a small container, remove, with a cotton moistned in thinner clean the thread, electrode, dry well, regap and tight again. You can take a wooden/plastic shushi stick and make yourself a big cotton swamp, damp with thinner and clean well in circles the cylinder head thread. Will look like brand new.

Happy Boating

[ian parkes]

Originally Posted by Locozodiac

Ian, what solvent do you use or recommnd for cleaning.

Have benn cleaning plugs with Acrylic Thinner for years with excellent results. Dip/soke the plug electrode and all the extension of the thread for 30 secs in a small container, with a cotton moistned in thinner clean the thread, electrode, dry well, regap and tight again. You can take a wooden/plastic shushi stick and make yourself a big cotton swamp, damp with thinner and clean well in circles the cylinder head thread. Will look like brand new.

Happy Boating

Thinners is ok I guess , i usually grab a tin of carb cleaner spray , which smells just like thinners .
Petrol is always to hand I suppose that would sort an oily plug .

I haven't seen an oiled plug for years but i used to clean them in petrol then burn it off with a lighter , a warm plug used to help if you could get it back in quick enough . I don't miss those days really.

[BogMonster]

Originally Posted by Locozodiac

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.

I always try and have a short blast at WOT as late as I can before I take the boat out of the water - I figure that if the plugs are clean it will start better the next time I use it, and my engine is prone to fouling one plug all the time anyway (not sure why)

[Locozodiac]

Originally Posted by BogMonster

I always try and have a short blast at WOT as late as I can before I take the boat out of the water - I figure that if the plugs are clean it will start better the next time I use it, and my engine is prone to fouling one plug all the time anyway (not sure why)

Yes, sometimes wot (2 stroke engines) before taking the boat out until the engine stops out of gas, specially if don't know when will be the next go out. Iy you are a person that removes engines from small boats and lays engine inside car trunks will definitely avoid the gas/oil spillage inside. Your carpet will appreciate it the most...

From all years cleaning spark plugs, have noticed that the lower plug always tend to foul more than the upper in 2 cylinders 2 strokes engines. That's why in the next cleaning session are regaped and rotated to the opposite cylinder. Have given me better plug life span between changes and probably avoid shorts on plugs.

Happy Boating