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Old 02-21-2006, 09:37 PM   #1 (permalink)
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Fouling front spark plug

I am having a strange problem. I have a chopper with a 124 inch S&S. I just reciently performed some changes on the bike including a vance and hines exhaust, new spark plugs and 8mm ignition wires. My problem is now that the bike is all back together the front cylinder is getting very hot almost immediatly after I start the bike and is turning the plug black. The rear cylinder seems to be running normal. The bike sounds like it is running great though. Please Help!
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Old 02-22-2006, 08:26 AM   #2 (permalink)
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I'm not sure the two are necessarily related. Given your fuel/air mix is correct, maybe you have a bad guide seal and oil is coloring the front plug. As far as the front warming first, that's a characteristic of the common manifold (even on injected bikes). The front always seems to be richer at idle, but then goes lean at speed. What I've noticed anyway.

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Old 02-23-2006, 03:39 PM   #3 (permalink)
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Quote:
Originally Posted by BM3flitedog
I am having a strange problem. I have a chopper with a 124 inch S&S. I just reciently performed some changes on the bike including a vance and hines exhaust, new spark plugs and 8mm ignition wires. My problem is now that the bike is all back together the front cylinder is getting very hot almost immediatly after I start the bike and is turning the plug black. The rear cylinder seems to be running normal. The bike sounds like it is running great though. Please Help!
What KKrider said....

Is the plug a dry, sooty black, or wet and oily? If it's dry, go to the next paragraph. If it's wet, call the builder of the engine. It'll need some top end repairs.

Check for an intake leak. Spray some WD40 (use the red nozzle) around the flanges (carb and head ends) while it's running and you will hear the rpm change slightly if there's a leak. My guess is that the rear cylinder is leaking causing the front cylinder to run richer and hotter.

The next, and most important step, is to put it on a dyno to get it tuned properly with an AFR gauge. That's the only way to get the mixture correct across the whole rpm range. This is something that must be done whenever you change the induction or exhaust systems.

Another thing... are you using the S&S carb? If you are, do not use the enricher (choke)!! You'll be fouling plugs regularly if you use it too much. I only use mine if it's less than 20 deg. F. outside, and even then for no more than 30 seconds. That's about the only flaw with the S&S carbs. Other than that, they perform great!

Last edited by ToddM; 02-23-2006 at 03:45 PM.
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Old 03-01-2006, 08:55 AM   #4 (permalink)
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Any luck fixing the problem?
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Old 03-02-2006, 12:01 PM   #5 (permalink)
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Quote:
Originally Posted by BM3flitedog
I am having a strange problem. I have a chopper with a 124 inch S&S. I just reciently performed some changes on the bike including a vance and hines exhaust, new spark plugs and 8mm ignition wires. My problem is now that the bike is all back together the front cylinder is getting very hot almost immediatly after I start the bike and is turning the plug black. The rear cylinder seems to be running normal. The bike sounds like it is running great though. Please Help!
If you had a intake leak both plugs would be dark...where its just your front plug and you just installed a exhaust pipe you probably have a exhaust leak in front ...look close see if any soot around pipe where it enters head....that would make it run hot,,,may also get popping letting off gas or blow black smoke
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Old 03-02-2006, 09:09 PM   #6 (permalink)
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Quote:
Originally Posted by plasterhead
If you had a intake leak both plugs would be dark...where its just your front plug and you just installed a exhaust pipe you probably have a exhaust leak in front ...look close see if any soot around pipe where it enters head....that would make it run hot,,,may also get popping letting off gas or blow black smoke
Not if only one of the intake seals was leaking. If only one is leaking, then each plug will be a different color, depending on which plug that was being read to adjust the mixture. Same thing happens on the dyno... the AFR sensor is only put into one of the pipes, so if you tune it to one cylinder, then the other will either be lighter or darker, depending on which one was leaking. If the mixture is too rich, that cylinder will run hot and the exhaust pipe will start to discolor due to fuel still burning in the pipe on the way out of the head. If it is running too lean, it will still overheat the cylinder, but the plug will be white instead of black. If the exhaust has a leak, then yes, it will cause popping on decel. You might also hear it leaking, sounding almost like a bad lifter.

Last edited by ToddM; 03-02-2006 at 09:15 PM.
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Old 04-23-2006, 09:30 AM   #7 (permalink)
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Quote:
Originally Posted by BM3flitedog
I am having a strange problem. I have a chopper with a 124 inch S&S. I just reciently performed some changes on the bike including a vance and hines exhaust, new spark plugs and 8mm ignition wires. My problem is now that the bike is all back together the front cylinder is getting very hot almost immediatly after I start the bike and is turning the plug black. The rear cylinder seems to be running normal. The bike sounds like it is running great though. Please Help!

so what did you find out intake or exhaust leak
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