Front cylinder running rich
Front cylinder running rich
When I went to change plugs this spring (as well as last spring) I noticed that the front cylinder plug was a little darker and partially black on one side of the electrode but the other side was almost the proper light brown. Where the rear plug looked perfectly even in color over the whole electrode. Is this common for an EVO with 50K+ miles on it? The bike runs fine and always starts without a problem. I've got a S&S Super E shorty, Screamin Eagle ignition and a dyna coil if that helps.
Road Warrior
Joined: Apr 2007
Posts: 1,354
Likes: 1
From: S.W. Florida
alaskajeff,
I'm kind of interested in the replies you receive. Mine's just the opposite, the rear cylinder is a bit rich and the front is perfect. The Dyno says that the advance curve and jetting on my S&S carb are perfect.
I'm kind of interested in the replies you receive. Mine's just the opposite, the rear cylinder is a bit rich and the front is perfect. The Dyno says that the advance curve and jetting on my S&S carb are perfect.
Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
If you have a valve seal just starting to go it will leak and "mist" one side of the electrode. This will make it darker. As it gets worse the black will get wet. Or if a valve is starting to leak it can "lean out" one side of the electrode.
HDF Community Team
Joined: Dec 2005
Posts: 5,422
Likes: 2,621
From: NC USA
Yeah, mine was always darker on the rear and with stock ignition, the rear is timed about 2 degrees lower. A true dual exhaust conversion made my rear plug a bit lighter and the ignition I'm running now has it cleaner than the front, but head temps differentials are still typical.
Road Warrior
Joined: Apr 2007
Posts: 1,354
Likes: 1
From: S.W. Florida
I know that you are generally correct with these types of things. New ported SE heads with Cometic Viton seals and new CP pistons and rings with about 1K on them. The rear plug is a bit sooty, but it's not oil residue. Compression and leakdown tests were on the money. Thinking about checking the accelerator pump on the S&S over the weekend to see where it's pointed as the carb was polished and rebuilt at the same time. Might also try replacing the Dyna 2000 module with my spare Crane HI-4 and see what happens there. What do you think??
Last edited by Buddy WMC; May 1, 2009 at 05:04 AM.
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Elite HDF Member
Joined: Sep 2007
Posts: 4,468
Likes: 12
From: Bluffton, South Carolina
Buddy,
If all was done correctly then I would also check the nozzle and while I was at it I would also re-torque the manifold. Were the SE heads ported aftermarket? Some times a difference in flow or velocity will cause this also. You could try the Crane unit and play with the rear cylinder timing (keep it under two degrees) to see if that helps.
If all was done correctly then I would also check the nozzle and while I was at it I would also re-torque the manifold. Were the SE heads ported aftermarket? Some times a difference in flow or velocity will cause this also. You could try the Crane unit and play with the rear cylinder timing (keep it under two degrees) to see if that helps.
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