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I am usually pretty good at reading the plugs. I have no problem doing plug chops, etc. I can tell lean from rich no problem. The question that I have is basically what if there are conflicting readings. For example, specifically: a few times I have had plugs show a nice white insulator fully indicative of a lean condition but around the steel barrel and on the tip it shows sooty deposits indicative of a rich condition.

This has happened on several of my bikes, from SOHC CB750's to old Triumph twins to BMW airheads, etc. The riding conditions are usually suburban and two lane riding with occasional blasts on the interstate....nothing abnormal. Am I looking at different and dissonant carb circuits?

By the way, there is no specific bike that this an acute problem with.....YET!

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Maybe richness, or at least incomplete combustion, when it idles for a few seconds before you stop the engine.

Probably doesn't matter.

I expect you know to kill the engine at speed, without closing the throttle first, when doing plug chops.


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What type of fuel(s) are you using?

Ethanol blends? Octane rating(s)?

Are you seeing dark/dull fuel residue or shiny black oil residue?

Gray or white ash?

Last note... The chops are read at the base of the insulator, and not at or near the tip.

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Am I looking at different and dissonant carb circuits?

You're looking at modern fuels. I haven't seen clean rims and tips since about 1990. Same bikes, same tuning. Now you just have to go by the porcelains.





Mark Z

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Yes, I agree with Mark.

If I knew how to post PDFs I'd post this technical note released by BP in 2002 on converting from RF100 (racing fuel 100- basically 100 octane avgas) to unleaded fuel. I've quoted some sections from it at the bottom.

At the time there was a lot of concern about the ability to 'tune' by plug reading. I think in the intervening period a lot has been learnt about how to adapt. Or it has become clear what the correct procedure is and that it's more critical with unleaded fuels. I have no experience with ethanol as I stay away from it (unless its in my fuel and I don't know). Seems to me from everything I've read that it's not just a matter of looking at the plug, but as the Z-man says, technique of 'reading' the plug is more important then ever. As is using the plug signs to interpret heat-range (# of blackened threads), timing (mark on ground strap) etc.


I put asterisks around a useful bit of info. Seems the fuel companies advise that soot anywhere but the insulator is normal.


Probably telling you stuff you know.

Ray


"Racing 100 has significantly higher lead content than Premium Unleaded Petrol. The lead
and the chlorine and bromine scavengers combined with the lead are used to lower the
burnoff temperature of carbon so that spark plugs and engine surfaces could be naturally
cleaned at relatively low temperatures. Without these scavengers, the carbon burns off when
it gets to around 450 – 500 degrees C. The exhaust pipe is black when running on unleaded
petrol and white or grey coloured when running on a leaded fuel because the lead oxide
deposits out in the pipe. For the same reason spark plugs will be black when running on
unleaded petrol because there is no white oxide coating."

"Note, spark plugs from a correctly tuned engine using unleaded fuel are often coated with a
thin black deposit. Fouled plugs ******have thicker black deposits which also cover the insulator******,and often have a wet appearance.
The lead in leaded fuel helped to catalyse carbon burnoff during engine warmup. Now that
lead has been removed from the fuel, carbon burnoff (self cleaning) requires a higher
temperature."

"The following notable changes will be detected:
• No longer will the bike produce a “grey” exhaust pipe. In the past, many motorists tuned
their bike by the colour of the exhaust pipe. This “grey” was caused by the laying down of
lead oxide deposits in the exhaust. As there is no lead in LRP, exhaust pipes will look
“black” as with Unleaded .
• Spark plugs will no longer have a white coating of oxidised lead but will be black,
irrespective of the temperature of the engine."

"Spark Plugs - Check condition of electrodes and ceramic insulator. Check electrode gap.
Plugs with carbon coating their insulators can sometimes be cleaned. If the carbon has
penetrated the pores of the insulator, grit blasting may not be effective and the plugs will need
to be replaced.
Check that plugs are of the recommended type and heat range.
If vehicle is used mainly for short trips and is not also used for long distance, high speed
running, consult the spark plug agency about fitting hotter plugs."






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Quote

• Spark plugs will no longer have a white coating of oxidised lead but will be black,
irrespective of the temperature of the engine."


Not true, I have removed dozens of plugs from all sorts of engines running on unleaded and they all had some sort of non black color, some were bone white...
The spark plugs in my race Triumph run near bone white on the whole insulator...A thin band of dull black at the end of the screw shell.The ground electrode discolored about halfway. VP leaded race fuel is used.......But I don't jet the bike engine by looking at the plugs..
From what I'm told the color on the end of the plug insulator near the center electrode is an indication of part throttle fuel mixture..


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
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knuckle head
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This plug guide applies to full throttle readings on clean plugs.

Plug reading full throttle



61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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...I think that most users, and that s about 80% of us, will not crank up the bike (depending on the model) to 130kms/h or more and then kill it...you need a very nice clutch operation and balls to do it with all these traffic; to say something, if the bike is very old like mine and something happens...the truck or car behind would hit you no doubt.
Most do not have access to circuits or dyno.
saying that, the insulators in both of what I have are white/brownish with a shade of grey.


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