Reading a spark plug
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Road Warrior
Joined: Sep 2007
Posts: 1,252
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Reading a spark plug
This is the front cyclinder plug out of my 2003 Road King Anniversary. Stage one and using high test fuel. This is after a 50 mile ride this morning. I never pulled the rear plug but I doubt it will be much different. I have heard a lot about reading plugs. The colour of the insultator and where the heat line is on the ground bar. What does everyone think about this plug. I'm used to shovelheads and ironheads and a nice tan brown was always the default for plugs but this newer style bike I'm not sure of.
randy
randy
Tourer
Joined: Jul 2010
Posts: 284
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From: Belfast, N. Ireland
Extreme HDF Member
Joined: Jun 2011
Posts: 14,731
Likes: 2,536
From: Mountain Top, Alabama
Looks like mine did yesterday when I pulled them after 25,000 miles.
Cleaned, checked gap, reinstalled.
Why mess up a good thing? Hit 'em with a clean wire brush, and ride.
Champion has a most excellent chart that can be found online...
Cleaned, checked gap, reinstalled.
Why mess up a good thing? Hit 'em with a clean wire brush, and ride.
Champion has a most excellent chart that can be found online...
Extreme HDF Member
Joined: Sep 2010
Posts: 14,744
Likes: 402
From: Phoenix '53, '88, '09 Big Twins
reading plugs belongs with carbs and points.
all those charts are based on photos taken 30 years ago.
fuel additive packages have also changed greatly and the detergents, octane ( knock inhibitors- lead is gone) and ethanol will make for great variation from what was considered 'common knowledge'
mike
all those charts are based on photos taken 30 years ago.
fuel additive packages have also changed greatly and the detergents, octane ( knock inhibitors- lead is gone) and ethanol will make for great variation from what was considered 'common knowledge'
mike
Road Warrior
Joined: May 2005
Posts: 1,301
Likes: 24
From: Minden LA
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Road Captain
Joined: Nov 2007
Posts: 697
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From: Magnolia, DE
Agreed. You have got to put anti seize on those threads!!!
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Tourer
Joined: Jul 2010
Posts: 284
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From: Belfast, N. Ireland
Whilst agreeing with some of the comments regarding new fuels etc, the color of the deposits on a spark plug STILL gives a good indicator of an engine's running. Even in the age of ECUs, they can still get air mixtures wrong!!
From the service manual:
Compare your observations of the plug deposits with the descriptions provided below.
a. A wet, black and shiny deposit on plug base, electrodes and ceramic insulator tip indicates an oil fouled
plug. The condition may be caused by one or more
of the following:worn pistons, worn piston rings, worn
valves, worn valve guides, worn valve seals, a weak
battery or a faulty ignition system.
b. A dry , fluffy or sooty black deposit indicates an airfuel mixture that is too rich.
c. A light brown, glassy deposit indicates an overheated
plug. This condition may be accompanied by cracks
in the insulator or by erosion of the electrodes and is
caused by an air-fuel mixture that is too lean, a hotrunning engine, v alves not seating or improper ignition
timing. The glassy deposit on the spark plug is a
conductor when hot and may cause high-speed misfiring. A plug with eroded electrodes, heavy deposits
or a cracked insulator must be replaced.
d. A plug with a white, yellow, tan or rusty brown
powdery deposit indicates balanced combustion.
Clean off spark plug deposits at regular intervals
From the service manual:
Compare your observations of the plug deposits with the descriptions provided below.
a. A wet, black and shiny deposit on plug base, electrodes and ceramic insulator tip indicates an oil fouled
plug. The condition may be caused by one or more
of the following:worn pistons, worn piston rings, worn
valves, worn valve guides, worn valve seals, a weak
battery or a faulty ignition system.
b. A dry , fluffy or sooty black deposit indicates an airfuel mixture that is too rich.
c. A light brown, glassy deposit indicates an overheated
plug. This condition may be accompanied by cracks
in the insulator or by erosion of the electrodes and is
caused by an air-fuel mixture that is too lean, a hotrunning engine, v alves not seating or improper ignition
timing. The glassy deposit on the spark plug is a
conductor when hot and may cause high-speed misfiring. A plug with eroded electrodes, heavy deposits
or a cracked insulator must be replaced.
d. A plug with a white, yellow, tan or rusty brown
powdery deposit indicates balanced combustion.
Clean off spark plug deposits at regular intervals
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