Spark plug fail

[Dave Sherman]

Had a strange failure of a spark plug today. Giving my Powerhouse generator its monthly exercise, and it's usually a bit temperamental to start it, especially when it gets cold. Auto choke pulls off too quickly and it stalls a few times. This time it flooded, and I eventually exhausted the battery trying to start it. Then it finally didn't show any signs of coughing even when I was using the rope starter. Finally yanked the spark plug, which was wet and looked a little black. I cleaned it up a little, plugged it in, grounded the shell, pulled the rope, and... No spark.

Grabbed a spare plug I had, and yes, there is spark again. Put the fresh plug in, and it started right up. Then I was trying to figure out what happened to the old plug. Sprayed some carb cleaner and wiped the soot off, but it still wouldn't show any spark. Then I looked into the end and saw that it was sparking faintly, except it was inside between the body of the plug and the insulator around the center electrode. No wonder it was having problems! So, what could cause this? I'm guessing it has a crack in the insulator, although it appears to be intact.

 

[berniedd]

Cracked insulator around the center electrode.

 

[mrsilv04]

'Torch' brand spark plug?

 

[ddtmoto]

Wet fouled. Fairly common in carburetored seldom used machines. Keep a spare for days like this.

 

[Whimsey]

Originally Posted By: mrsilv04
'Torch' brand spark plug?


Are you picking on those "fine quality" Torch spark plugs? I'm shocked, I say shocked

s/o. I have one in my snow blower that I bought new last year. This week I'm going to fuel up the blower and see how well it starts from dry. In all honesty the snow blower ran like a top with the torch plug last year, of course it was new. I have a new NGK as a spare if the Torch fails me this year

. Ironically replacement Torch plugs are $3 to $4 more than the NGK.

Whimsey

 

[eljefino]

If you have a wet fouled plug, heat its tip with a propane torch and stick it right back where it came from. A "hot plug" lights off better.

I suspect your fuel is going bad, as the carburetor won't vaporize it all that well, and it's turning into gas droplets instead.

 

[Dave Sherman]

Originally Posted By: mrsilv04
'Torch' brand spark plug?


Interestingly, it was the NGK that had replaced the original Torch plug. Had to put the spare Torch plug in to get it running.

How does wet fouling cause the spark to jump through the ceramic insulator though? I'm leaning more toward cracked insulator, but what could cause it to crack?

 

[flatlandtacoma]

I'm guessing it's cracked. As to why? May have been dropped, could be a manufacturing defect. Hard to say.

It wouldn't scare me away from NGK plugs unless it happened again.

 

[spackard]

Wet fouling is seen, for example, in motorcycles (with two-stroke engines). With oil and gasoline covering the carbon that has adhered to the firing end, the insulation resistance value drops abruptly, causing misfires.

 

[TFB1]

Originally Posted By: spackard
Wet fouling is seen, for example, in motorcycles (with two-stroke engines). With oil and gasoline covering the carbon that has adhered to the firing end, the insulation resistance value drops abruptly, causing misfires.


This^^^

A old trick is pull the boot just far enough off the plug till spark has to jump maybe 1/8", if just wet fouled the spark will usually jump the tip gap as well... That's a leftover from days of carburetors and points ignition... Beats the [censored] out of pulling plugs to dry them off...

Last time I remember using it was on a early '80s Chevette that had fouled all it's plugs(we'd just set the all time record low of -2*F that still stands)... Due to space limitations I could only easily access three plugs so pulled boots back on those and it started almost instantly, but skipped on the fourth till it had run 15-20 seconds...