plug color
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Stellar HDF Member
Joined: Apr 2009
Posts: 3,039
Likes: 11
From: Northern Ontario
plug color
While doing some upgrades on the engine I removed the plugs to roll engine for pulling adjustable pushrods and I noticed the rear plug is darker than the front plug.Last year I changed ignition to Dynatek 2k, not sure if this can have anything to do with it.I don't think I could have a tight pushrod, new lifters last year as well. The heads were rebuilt when I did the rest of the motor. Is a dark plug especially in the rear anything to be concerned about? I know the rear generally will run hotter because of lack of air flow.
Ideas?
Ideas?
Road Warrior
Joined: Dec 2007
Posts: 1,286
Likes: 64
From: SoCal
One would think that the rear cylinder runs hotter but I read on this or another forum that a guy checked his cylinders temps with an IR gun and the rear was actually running cooler than the front.
I don't believe he was having problems, he just wanted to see what temps they were running at.
Bottom line, if your bike is running well, I would not sweat the rear plug being darker than the front as long as it is not oil or fuel fouled.
I don't believe he was having problems, he just wanted to see what temps they were running at.
Bottom line, if your bike is running well, I would not sweat the rear plug being darker than the front as long as it is not oil or fuel fouled.
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,070
Likes: 2,115
From: Ohio
In the tuning section of another forum, a documented carb tuning thread with a Wego afr reading system in each 02 sensor recorded different afr's between cylinders and it has been common since the Shovel days so don't sweat it and throttle on 
EFI is easy to make the cylinders equal but carbs takes the hidden intellegence of "Rainman" to make carb cylinders fire equal, Nascar head programs is an example of these Einsteins.
EFI is easy to make the cylinders equal but carbs takes the hidden intellegence of "Rainman" to make carb cylinders fire equal, Nascar head programs is an example of these Einsteins.
Last edited by 1997bagger; Jan 8, 2012 at 12:05 PM. Reason: Can't spell worth a crap
Stellar HDF Member
Joined: May 2009
Posts: 2,856
Likes: 127
From: Middle of Kansas
Don't know if they still do it on EVO's, but on the older engines the timing was retarded slightly on the rear cyl. to let them run cooler. That would also make the rear plug run a little darker. As long as it is just color, and not wet with oil, I would not worry about it at all.
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Stellar HDF Member
Joined: Apr 2009
Posts: 3,039
Likes: 11
From: Northern Ontario
Don't know if they still do it on EVO's, but on the older engines the timing was retarded slightly on the rear cyl. to let them run cooler. That would also make the rear plug run a little darker. As long as it is just color, and not wet with oil, I would not worry about it at all.
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