Author Topic: Reading a plug?  (Read 894 times)

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Offline Curtis

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Reading a plug?
« on: May 20, 2019, 10:09:17 AM »
Doing some jetting here. So I understand the basics of the colouring but what about when you have two colours like black/sooty around the edge and very white in the middle insulator tip? Im thinking lean at WOT and rich at low rpm. Whats peoples thoughts?

Offline matcho mick

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Re: Reading a plug?
« Reply #1 on: May 20, 2019, 06:34:37 PM »
sounds about right  :P
work,the curse of the racing class!!
if a hammer dosn't fix it,you have a electrical problem!!

Offline bazza

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Re: Reading a plug?
« Reply #2 on: May 21, 2019, 07:25:13 AM »
Guessing that timing and plug heat range correct? and air filter clean.
I would go richer on main Jet, start up and ride around at medium pace for a while then do your WFO run,clutch in and kill motor.Now check plug
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Offline Curtis

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Re: Reading a plug?
« Reply #3 on: May 21, 2019, 09:20:57 AM »
Yes everything healthy and inspec....thanks

Offline GMC

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Re: Reading a plug?
« Reply #4 on: May 22, 2019, 07:34:23 PM »
Discount Motorcyle Wreckers will have a range of emergency spares at the A3VE for those that need
If you give Paul a call he might be able to have a barrel and piston on standby for you ;D
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Offline TT5 Matt

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Re: Reading a plug?
« Reply #5 on: May 23, 2019, 02:43:46 AM »
an old tuner that loved bombing out old pommy bikes told me to start fat/rich  everywhere and go down that way no holed/seized pistons or burnt valves,worst case youll foul a plug which is a lot cheaper then ruining your newly rebuilt top end

Offline Curtis

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Re: Reading a plug?
« Reply #6 on: May 23, 2019, 09:13:29 AM »
I doubt he has NOS needles and emulsion tubes for a TT350.. :-[


Discount Motorcyle Wreckers will have a range of emergency spares at the A3VE for those that need
If you give Paul a call he might be able to have a barrel and piston on standby for you ;D

Offline arwtee

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Re: Reading a plug?
« Reply #7 on: November 24, 2019, 06:51:15 PM »
White in the middle and sooty black around the edges sounds to me like the wrong heat range plug. I suspect you need a plug where the tip runs cooler.

Offline Watto HVA 1

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Re: Reading a plug?
« Reply #8 on: November 26, 2019, 04:02:06 PM »
this from the Klemm Vintage page..

About “Plug Reading” -  In the 1970s spark plug “reading” was a very commonly used means of fine tuning race engines.  Sadly, this method was only valid for main-jet setting, and it required that the rider get a clean “plug-chop” (simultaneously shutting off from full-throttle, and hitting the kill button while at peak rpms in high gear).  If you do not have a clean plug chop, the plug reading is useless.  In later years, the real time deto-sensors introduced in the 1990s made plug reading a Neanderthal means of fine tuning, and no professionals do it anymore.  It also bears noting that today’s pump gasolines (laden with oxygenates and varying ethanol percentages) do not “color” spark plugs nearly as quickly as race gas (or 1970’s pump gas).  The long time it takes today’s pump gas to properly color a plug is even more reason to not bother with reading plugs.  There is certainly validity to looking at the spark plugs on a regular basis just to confirm the there are no internal catastrophes in progress.  But for fine tuning, plug reading is a process that takes up so much time and offers such questionable precision, no professional tuners rely on it anymore.   Another tuning fable that still surfaces occasionally is that different areas of the spark plug tip/electrode are indicators of various low speed jetting ranges.  This is absolutely untrue, and it always has been untrue.

Offline oz555ktm

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Re: Reading a plug?
« Reply #9 on: November 26, 2019, 08:27:47 PM »
This is a Old Spark Plug  Chart that has been Good over the Years

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Offline Curtis

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Re: Reading a plug?
« Reply #10 on: December 03, 2019, 08:59:16 AM »
Now that is very interesting ..thanks for the input
this from the Klemm Vintage page..

About “Plug Reading” -  In the 1970s spark plug “reading” was a very commonly used means of fine tuning race engines.  Sadly, this method was only valid for main-jet setting, and it required that the rider get a clean “plug-chop” (simultaneously shutting off from full-throttle, and hitting the kill button while at peak rpms in high gear).  If you do not have a clean plug chop, the plug reading is useless.  In later years, the real time deto-sensors introduced in the 1990s made plug reading a Neanderthal means of fine tuning, and no professionals do it anymore.  It also bears noting that today’s pump gasolines (laden with oxygenates and varying ethanol percentages) do not “color” spark plugs nearly as quickly as race gas (or 1970’s pump gas).  The long time it takes today’s pump gas to properly color a plug is even more reason to not bother with reading plugs.  There is certainly validity to looking at the spark plugs on a regular basis just to confirm the there are no internal catastrophes in progress.  But for fine tuning, plug reading is a process that takes up so much time and offers such questionable precision, no professional tuners rely on it anymore.   Another tuning fable that still surfaces occasionally is that different areas of the spark plug tip/electrode are indicators of various low speed jetting ranges.  This is absolutely untrue, and it always has been untrue.

Offline sleepy

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Re: Reading a plug?
« Reply #11 on: December 05, 2019, 11:03:11 AM »
Sorry for the late response but I've been in for more back surgery.
Probably need to tell us what sort of motor and what it is being used for as 2 and 4 strokes will so different things in the plug.
With unleaded pump fuel the plug will always be black around the edge as is the entire inside of the combustion chamber after it has been run for a while. The colour of the insulator will go black if it very rich but it takes some time. The insulator can also be black and shiny if it is to lean in a 2 stroke, sounds wrong but if the plug is getting hotter than normal the oil in the fuel will bake onto the hot surface sending it black. I have seen quite a few motors recently that have seized after the owners got advice from the pits expert "mate your plug is black it's way to rich go down in main jet" next outing they do a top end and when it gets to me every thing in the top end is baked black from the heat.
So my advice is to be very cautious with plug colour.