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Old 11-02-2019, 05:25 PM   #1
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Default Plug reading tip

Iíve seen a number of posts recently about plug colour / tuning, where itís been noted that modern fuel doesnít allow plugs to be Ďreadí using the diagnostic charts you see.

I picked this up yesterday from a guy who seemed to really know his stuff - Dave Plumb at M.E.S.S, I visited on a tip off from thefrenchowl (thanks, Patrick).

Take a large clear container, eg.,

Fit a tap at the bottom. Fill with fuel, and add a couple of cups of water. Slosh around, wait an hour, then drain off the water which has settled at the base of the container using the tap.

The water has absorbed the ethanol in the fuel making it useful for reading plugs (or if you want to do it regularly, not messing up all the other fuel components ethanol likes to eat).

Yet to try it but seemed like a good tip to pass along.
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Old 11-03-2019, 05:41 AM   #2
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Default Re: Plug reading tip

Are you removing the ethanol then using the fuel in your bike? If so, removing the ethanol also removes a few octane points..Like turns 93 US octane into 90.....
You can still read plugs running with E10 gas...However some brands of gas use additves to increase octane that can turn the plugs a reddish color...Otherwise, E10 will color the insulator about the same or slightly darker than non ethanol.

Those old charts showing insulator color are really for part throttle only, full throttle readings are from deep inside the insulator and carbon on the steel shell..
This plug is from my modified Triumph T140.The fuel is non ethanol pump gas.This was a new NGK plug removed after about 15 miles of high speed heavy throttle on the back roads..Many here might say it's too lean...It's not's actually a tad rich...The discoloration on the ground strap inicates the plug is just a touch too cold..
Lots of opinion on this stuff of course.

I ride junk,some of it is fast
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Old 11-03-2019, 08:23 AM   #3
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Default Re: Plug reading tip


Spot on.. My UL looked like it's running lean when after 2000 miles turns out it was a tad rich, I leaned it out a little and it pulls a lot harder! even though.. using my father (Old timer) he was telling me it was lean also!
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