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  What causes pulgs to foul?

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Author Topic:   What causes pulgs to foul?
SWarren posted 04-25-2002 09:28 AM ET (US)   Profile for SWarren   Send Email to SWarren  
What are some reason for plugs to foul? Water in the cylinder, to hot, to much oil? If you foul plugs what can you do to see why they foul? Just curious, I was reading the OMC manuel and they mention fouled pulgs as a reason for poor running engines, but no causes of why pulgs foul in the first place.
Duncan posted 04-25-2002 04:21 PM ET (US)     Profile for Duncan  Send Email to Duncan     
I'm no mechanical guru but I've heard that extended slow speeds (trolling) will
foul plugs.

I pull mine and clean with a coarse cloth and gasoline. In a pinch, on the old motor I use for duck hunting, I use a little fin sandpaper.

Remember, They're only three bucks a piece. I alwaws cary a spare set.

triblet posted 04-25-2002 07:42 PM ET (US)     Profile for triblet  Send Email to triblet     
The usual cause for fouled plugs is a rich
mixture (too much gas for the volume of air).
This is carburation/injection problem.

It can also be caused by oil fouling.


Ron Brassord posted 04-26-2002 08:37 AM ET (US)     Profile for Ron Brassord  Send Email to Ron Brassord     
I recently got a tip from an experianced boat mechanic that the best way to clean a spark plug was to use brake parts cleaner. A wire wheel or other scrapers could cause more damage than help. I bought a spray can and tried it, and the plugs come out like new with a few squirts, especially up inside the base. A $2.00 can lasts forever, and has many other uses around a boat.
Good boating Ron B
rb posted 04-26-2002 11:03 AM ET (US)     Profile for rb  Send Email to rb     
I wonder if 4-strokes are less likley to foul plugs at trolling speeds then 2-strokes?
where2 posted 04-26-2002 12:37 PM ET (US)     Profile for where2  Send Email to where2     
Realistically speaking, if you were to troll, and never open the engine up, you could modify your plug selection to keep them cleaner by chosing a hotter plug. The problem with running a hotter plug at middle throttle and WOT is predetonation (pinging) which is not good for any engine (2 stroke, 4 stroke, or wankel). The manufacturers have had to choose the best compromise plug for all around performance. If you were racing, you'd choose a much different plug than if you wanted to troll all day.

Generally, the fouling I have seen was due to oil which was not completely combusted and left excess carbon on the plug tip. Eventually, the carbon produces a conductive path which is easier to travel than jumping the electrode gap.

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