mattb348

Member
Aug 2, 2005
204
0
I just got done reading the sticky plug reading 101 thread. Great thread!

I was curious about a couple of things though:

A. I noticed that it was stated that the more lean a bike runs, the closer the "fuel ring" gets to the bottom of the insulator. WHAT is the bottom? the end towards the porcilin side of the plug? or the end that has the "gap" on it?

B. What is a good thickness for the fuel ring? and what color is it supposed to be? Is it supposed to be one consistant color all the way down the insulator? And does the color of the "nose" of the insulator even matter?

Lastly, is the "main" jet the only one you adjust to make the bike leaner/richer to test your plugs? Does anyone even bother with the "needle"?? what exactly is the "needle" for?

As you can see I'm new to tuning dirtbikes. Thanks for any info :)
 

Jaybird

Apprentice Goon
LIFETIME SPONSOR
Mar 16, 2001
6,452
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Charlestown, IN
Matt,
The carbon ring should be at the end of the plug that is closest to the procelin. The part you can't see well, located behind the plug threads.
A 1-3mm ring would indicate your main jet was about correct.
You may want to find a nice magnifying flashlight to be able to even see the ring.
The other circuits need to be tuned by other methods than reading the plug.

Since the needle effects more than one circuit, it is one of the most important tuning items. The clip controls how far the taper of the needle sits in the carb, which can allow you to immediately change from rich to lean, or visa-versa. The taper profile of the needle also has an impact on the performance. Folks experiment with many different taper cuts.
 
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