Fouled Plug

Message

TG2891 · #1 Post by **TG2891** » Thu Dec 04, 2008 2:43 am

At first I thought it was only me but when I started asking others I soon found out that no one really had an answer they were really sure was correct. So my question is? What exactly happens when you foul a plug?

Here is my guess:
Wet/raw fuel seeps around the electrode under the ceramic ignites and causes the ceramic, electrode or resistor to fracture causing week spark.

Thanks
TOM

thedeatons · #2 Post by **thedeatons** » Thu Dec 04, 2008 3:13 am

Too rich, meaning too much fuel in the mixture, so the plug is fouled with fuel -OR- Plug is not hot enough to properly burn tthe mixture, in which case you need a different plug. Typically each number increment on a spark plug means a 50 degree difference in combustion chamber temperature.

NRath · #3 Post by **NRath** » Thu Dec 04, 2008 5:22 pm

I've wondered that same thing, TG. What physically happens to the plug to cause it not to work. I've pulled solid black plugs out of lawnmowers, weedeaters, and ATV's that were still running(obviously rich). But I've had plugs foul in the dale in much better shape. So what physically happens to the plug to cause the failure? My thought was that the build up creates a path to ground. But there's not always alot of build up. So maybe your theory is headed the right direction.

MX Quad Dad · #4 Post by **MX Quad Dad** » Thu Dec 04, 2008 11:30 pm

Electricity (sp?) takes the easyest path (path of least resistance) the plug is built to make the easyest path across the gap. As you know when it jumps across the air gap it is a spark (arc?). there a more than one reasons why there would be a easyer path. cracked porciliyn (sp?), carbon tracking are a couple possibilties. But basicly the electrical currant is finding an easier path that it dosen't have to jump the gap. no jump = no spark. I don't know how you would prove it but, I have been told you can Have a plug with a good spark sitting on top of the head but, not have a spark under compression. I myself have had a engine that wouldn't run and plug checked good and after checking numerus things, put a new plug in and it fire right up.

TG2891 · #5 Post by **TG2891** » Thu Dec 04, 2008 11:32 pm

I would agree, a rich fuel condition will foul a plug. I know I have done it a number of times before I joined this site and learned how to properly start a C-Dale.
And the path of least resistance also makes sense to.
But what I am looking for is:
What physically happens to the plug that makes it fouled?
What cracks the ceramic?
If the plug is hot and cool gas hits it I can see the crack hapening but you can foul a cold plug too.
Why does too much fuel equate to a plug not being able to be used after it is fouled? Even if it is cleaned or dried.
Just because a plug cannot burn fuel at a moment in time, this renders a plug junk just because it is splashed with fuel. That does not make sense. There has to be something more to it than that.

Thanks
TOM

thedeatons · #6 Post by **thedeatons** » Fri Dec 05, 2008 1:35 am

Fouled Dale plugs come back to life after you clean them with carb cleaner or QD or something like that, then burn the cleaner off....

TG2891 · #7 Post by **TG2891** » Fri Dec 05, 2008 3:12 am

When you say burn them off. do you mean like with a lighter or propane torch?

thedeatons · #8 Post by **thedeatons** » Fri Dec 05, 2008 5:50 am

I usually light the cleaner on fire with whatever is on hand, but just a MAPP gas torch with no cleaner will work in a pinch.

TG2891 · #9 Post by **TG2891** » Fri Dec 05, 2008 7:22 am

Did not know that. Going to have to give that a try. Thanks for the tip.

UpsMan · #10 Post by **UpsMan** » Fri Dec 05, 2008 1:14 pm

I have never fouled a plug in a four stroke motor except once, that was my suzuki drz125. I took it out, dried it off, put it back, and it started right up.