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Correct Plug Color?


blaisew

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It's first tune up time on my new-to-me 2002 RT. The valve clearance was good except the intakes; one one side were slightly loose. The plugs, though, hmmmmmmm.

 

I'm used to looking for a light tan color as an indicator of a good running carburated engine. The plugs that I removed from the bike were very light gray, which I was taught means "lean". The bike came with a Techlusion which I have turned "off" to see how it runs without mapping assist. New plugs last night, run to breakfast this morning, pull a plug to check the color, and the color is still very light gray.

 

Is this a problem, or normal with fuel injection? I'm heading out on a long trip in three weeks, and a holed piston is not something I want to deal with between Torrey and Blanding. Thoughts?

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It's first tune up time on my new-to-me 2002 RT. The valve clearance was good except the intakes; one one side were slightly loose. The plugs, though, hmmmmmmm.

 

I'm used to looking for a light tan color as an indicator of a good running carburated engine. The plugs that I removed from the bike were very light gray, which I was taught means "lean". The bike came with a Techlusion which I have turned "off" to see how it runs without mapping assist. New plugs last night, run to breakfast this morning, pull a plug to check the color, and the color is still very light gray.

 

Is this a problem, or normal with fuel injection? I'm heading out on a long trip in three weeks, and a holed piston is not something I want to deal with between Torrey and Blanding. Thoughts?

 

Blaisew, hard to tell much with spark plug color anymore.. First off modern unleaded gasoline doesn’t color plugs like the older leaded gasoline did.. Any color that you get will probably be in the halo at the upper end of the porcelain.. Secondly, modern emission era fuel/air mixtures run to the lean side of best combustion so you will get lighter plug coloring when you are looking at what little color you have there..

 

The only way you can get an accurate reading is to install new spark plugs then make a high speed run (no idle & no mid throttle) ,, then do a high speed ignition cut using the kill switch,, then pull the clutch in & coast to a stop,, allow the cylinders heads to cool,, then pull the plugs & use a magnifying glass to view the plug porcelains..

 

If you are worried about lean combustion damage just look for signs of aluminum on the spark plugs ( a dead giveaway) , or any signs of spark plug electrode damage caused by improper burn..

 

Another sign of impending lean problems are the valve clearances tightening up due to valve recession from heat..

 

 

 

Twisty

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As Twisty said, trying to draw any conclusions by plug colors is no longer a valid technique in modern day engines.

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ShovelStrokeEd

Well, it is still a valid technique, just the colors have changed.

 

Trying to draw valid conclusion about mixture strength or spark plug heat range, regardless of the gas used, from an engine that is undergoing normal usage is an exercise in frustration. Partial throttle operation is vastly different from full throttle operation and idle is even worse.

 

It is still possible to tell some stuff from a sustained full throttle run followed by, as Twisty said, a plug chop. However, it will only work on a new plug that has been subjected to very little part throttle operation. Best place to obtain this is at a drag strip. Install new plugs, push the bike to the line, fire it and go. At the end of the track, pull in the clutch and hit the kill. Some brakes would probably be a good idea as well. Cool motor and pull the plugs. With a lighted magnifier, carefully examine the ring formed at the base of the center insulator where it meets the body of the plug. With about 10 years or so of doing this, you'll be able to draw a few conclusions. Looking at the tip of the insulator, unless it is flecked with aluminum will tell you nothing.

 

I just don't bother. Run factory plugs, toss 'em over your shoulder every 50K miles or so and you will be fine.

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Thanks for the input Twisty, and everyone else, and I'll shelve any further thoughts on the matter. Both new plugs (15 miles at 70 mph) and the old plugs at 18K had exactly the same color, and no deposits, so all must be working as designed.

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