Spark plug fouling


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Old 08-03-08, 12:15 PM
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Spark plug fouling

Hi!! I'm new here and have a plug problem. My front plug on my motorcycle keeps fouling. I've put 3 new ones in and they all fouled. I haven't even gone 20 miles! I put one in yesterday and ran it a bit in the driveway and today-it's fouled. It is running a bit rich because I've got too fat a jet in the carb.
Any ideas??
 
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Old 08-03-08, 12:55 PM
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not fouled/not working

Sorry, the plug isn't fouling-it's just quits working.
I'm getting spark as soon as I put in a new plug. but then it just fries the new plug. Plug is on front cylinder on a Harley
74" Shovelhead.
 
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Old 08-03-08, 01:00 PM
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It would either be the coil = too hot or the wrong spark plug. If you're running the same plug on front and rear, it's probably the coil or a break in the plug wire = too hot a spark. Fuel/air mixture wouldn't do it that fast.

But what year is it, so we can dig up the configuration of the ignition system.
 

Last edited by marbobj; 08-03-08 at 01:23 PM.
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Old 08-03-08, 01:23 PM
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1979 Shovelhead

I put in a new Dyna coil recently and bored out 30 over with new pistons and rings. The plugs are the right ones. I once put in high-pro platinum plugs, thinking they'd be better, but the bike didn't like it, so I went back to Champion brand on advice from a Harley mechanic. I'm using Champion RN12YC that I bought from the Harley shop. It was running fine last season with the same plugs.
 
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Old 08-03-08, 01:28 PM
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See if the resistance on both plug wires are the same. If you have a break in a plug wire the coil will step itself up to jump the gap. The plug you're using is the Champion crossover for the 5R6A = Harley standard so it's not the problem.

Was it running on the same Dyna Coil last year or why did you change it? If the plug wires check out and the old coil was OK, I would swap the old coil back into it and see it that fixes it. If you were running too high of voltage into the coil, the coil would take the beating and heat up on you.
 

Last edited by marbobj; 08-03-08 at 02:41 PM.
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Old 08-03-08, 04:08 PM
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Coil was cracked

Thanks for the info. I replaced the coil because it was cracked, but working.(it's over at a buddy's right now so I can't replace it) I just put brand new plug wires in it too.
I will however check the resistance like you advised. Just went for a rip on it too (damn cold up here).
I'll let you know what I found out, right now I'm working on my Boat problem. The salmon are running, but my boat isn't!
 
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Old 08-03-08, 04:28 PM
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marbobj:resistance

I checked the resistance. They are different 5.3 Ohms on the front wire and 2.4 on the rear. But they are different lengths, significantly, so they would have different resistances.
Any other ideas?
I changed the coil due to electrical problems (old plug wires causing problems) and thought that replacing the cracked coil could make a difference along with new plug wires.
 

Last edited by ekbdfn99; 08-03-08 at 04:53 PM.
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Old 08-03-08, 05:38 PM
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Your total resistance would be relative to length, but the resistance value would be expressed as per foot. That resistance value should be stamped on the sheath, unless it's a solid core wire (metal all the way). If it is the latter, your resistance values are off. But from what you've got there, I can't see where that would affect the spark enough to destroy a spark plug that quickly.

You described the plugs as fried - do they show signs of scorching or do they simply quit working? Is the engine running well, then suddenly starts missing = one plug out while the other is still OK?

The coil, wires, plugs. Those are the only things at the end that's breaking. If you have an immediate fix by replacing the plug those three are where I would look. But three plugs in 20 miles - honestly I've never seen that in any internal combustion engine.

Combustion mixture - I would say highly unlikely unless you have a lot of oil passing the rings. But you would notice that.

You might try some of the Harley forums around and get some other specialized information. Really wish I could help you more. I hope you post back when you get it back on track, I'd like to know about it.
 
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Old 08-03-08, 05:50 PM
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Where are you for salmon fishing? For your bike - try this - will only take a second. Take the plug that you've pulled as dead and put in the running cylinder. Make sure it's actually dead.
 
 

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