What does a perfect plug looks like???

[MOTOMAX27]

I need some help.. My tri-z is running better than ever. but i dont want to be running it lean. My plug looks to light. I would like to see some pics of a nice running plug.. Thanks MAX

[Liquid-Darkness]

I read that a good jetted bike burns a brown tan color plug. Like the color of cardboard. This can be true but, its been known to jet up your main jet till your wide open throttle sputters in third gear, then jet one down
untill it clears up. That way you are as rich as you can get and be nowhere near lean. So start with stock jetting, then these tips should work.

[GPracer2500]

This plug is just barely rich:
http://www.dragstuff.com/techarticles/images/sparkplugs/AR3933-terry-wise-plug2.jpg

This plug is just barely lean:
http://www.dragstuff.com/images/plugs/10-29-05pass1-05.jpg

To get accurate plug readings you must use a NEW plug for the test. Warm the bike up on an old plug, change to a new plug, and immediately perform the test. It is important to spend as little time as possible at any throttle opening other than the one you are testing. For example, if you're testing your main jet--don't let the bike idle or ride around at half throttle. It only takes one or two 4th gear WOT passes for the plug to "color".

The reason those plugs look all messed up is because the threads have been cut away to allow viewing of the part of the plug that we're trying to see--THE BASE OF THE INSULATOR LOCATED WAY DOWN INSIDE THE THREADS. On many plugs the only way to see the "mixture ring" is to cut away the threads. This is were the term "plug chop" comes from. There are also special plug viewing tools that look a lot like the thing your Doc uses to look inside your ear.

In my experience, getting accurate info about a/f mixtures using plugs is widely misunderstood. Pulling out an old spark plug and inspecting it might give you a general sense if your jetting is even close, but it won't get you dialed in. What confuses many folks is that when you install a new plug, go perform the test, and inspect the plug, the tip of the insulator is usually still bone white--even if the jetting is WAY to rich. The trouble is that they are not looking at the correct spot on the plug. Again, it's all about the mixture ring at the base of the insulator. A used plug will have color all the way to the tip but the problem is that the color is the result of all the jetting circuits combined (and all manner of running conditions). You could be way to lean on your needle and pilot circuit and way to rich on your main jet and an old plug might look OK. Using an "average" of all possible throttle openings and running conditions is not the way to jet a carb.


Forget about plug reading charts like THIS ONE (http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp). Those are more to help you figure out why your lawn mower runs like junk. They will not help you decide between a 165 and 175 main jet. Only careful inspection of the mixture ring formed on a new plug will tell you that.

[MOTOMAX27]

thanks guys i will will let you know what happens

[x.system]

This plug is just barely rich:
http://www.dragstuff.com/techarticles/images/sparkplugs/AR3933-terry-wise-plug2.jpg

This plug is just barely lean:
http://www.dragstuff.com/images/plugs/10-29-05pass1-05.jpg

To get accurate plug readings you must use a NEW plug for the test. Warm the bike up on an old plug, change to a new plug, and immediately perform the test. It is important to spend as little time as possible at any throttle opening other than the one you are testing. For example, if you're testing your main jet--don't let the bike idle or ride around at half throttle. It only takes one or two 4th gear WOT passes for the plug to "color".

The reason those plugs look all messed up is because the threads have been cut away to allow viewing of the part of the plug that we're trying to see--THE BASE OF THE INSULATOR LOCATED WAY DOWN INSIDE THE THREADS. On many plugs the only way to see the "mixture ring" is to cut away the threads. This is were the term "plug chop" comes from. There are also special plug viewing tools that look a lot like the thing your Doc uses to look inside your ear.

In my experience, getting accurate info about a/f mixtures using plugs is widely misunderstood. Pulling out an old spark plug and inspecting it might give you a general sense if your jetting is even close, but it won't get you dialed in. What confuses many folks is that when you install a new plug, go perform the test, and inspect the plug, the tip of the insulator is usually still bone white--even if the jetting is WAY to rich. The trouble is that they are not looking at the correct spot on the plug. Again, it's all about the mixture ring at the base of the insulator. A used plug will have color all the way to the tip but the problem is that the color is the result of all the jetting circuits combined (and all manner of running conditions). You could be way to lean on your needle and pilot circuit and way to rich on your main jet and an old plug might look OK. Using an "average" of all possible throttle openings and running conditions is not the way to jet a carb.


Forget about plug reading charts like THIS ONE (http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp). Those are more to help you figure out why your lawn mower runs like junk. They will not help you decide between a 165 and 175 main jet. Only careful inspection of the mixture ring formed on a new plug will tell you that.

Great post GPracer, you should add that to the jetting 101 at the top of this page. I think alot of people know where to look but they don't know what to look for. I do my plug chops the same way when I'm running a motor hard or plan to. It may cost a few bucks to waste new plugs but when you want your motor to perform at its peak its a small price to pay.

[Yamahauler]

So if you were to jet it this way, would using a cheap plug like a champion to tune it affect the reading at all once you put a good quality plug in?

[GPracer2500]

So if you were to jet it this way, would using a cheap plug like a champion to tune it affect the reading at all once you put a good quality plug in?

As far as I know, cheap plugs are fine to use for testing.

[MOTOMAX27]

My plug looks like the first pic.. is that good??

[GPracer2500]

My plug looks like the first pic.. is that good??

It's rich, but not outragously rich.




Here's a couple more pictures to show the difference in coloring between a two size difference in main jet. These are from a 03 KX250. They were new plugs tested with a trio of 7 second WOT passes each. Care was taken to spend as little time as possible at anything other than WOT between installation and removal of the new plugs.

This was with a 148 main:
http://img62.imageshack.us/img62/4870/plug148mainmediumrh3.jpg

This was with a 152 main:
http://img62.imageshack.us/img62/1542/plug152mainmediumoi2.jpg

The 148 looks just right to me. The 152 would likely run fine (although at a slightly lower HP) but is unnecessarily rich.

The caveat about using plug readings to analyse air/fuel mixtures is that todays modern fuels--with all there additives, oxygenates, and whatnot--can produce funky readings. In two strokes, different pre-mix oils can change the outcome as well. When possible, it's best to jet using a/f data generated on a dyno (for four strokes) or EGT data interpreted by an experienced tuner (for two strokes). Once you KNOW your jetting is correct, chop a plug and see what it looks like. There's your baseline. Now when the weather or riding location changes your plug readings will have more meaning because you'll have a baseline to compare with.

That caveat aside, plug chops are useful for the casual tuner--just a pain in the ass to do. Most non-racers aren't going to go through the trouble of eliminating the variable of differing fuels and oils. And that's fine.

Just to give credit where it's due--these last two pics are from a fella named Keith LoCastro.

[MOTOMAX27]

Thanks buddy for the good info and the nice pics. So now i know my z is running really dam good and now with Mr. Sprock's billet head and his advice. You must hold on.