Simple Plug Reading 101

Never ever seen anyone put out info like that...

You sure Mickey wasn't telling you about TIMING and heat range???

That marking on the ground strap is an indicator of timing/heat range... not air/fuel ratio.


The marking on the ground strap can be looked at two ways...
If the marking is too far out towards the tip of the ground strap...

1- The plug is too cold for the tune...
2- The tune on the ignition timing could use a few more degrees of advance...

If the marking is too close to the base ring...

1- The plug is too hot for the tune...
2- The tune on the ignition timing could use a few more degrees of retard...



Now... air/fuel ratio "could" effect where the marking is somewhat...
After all, firing end TEMPERATURE is what causes this marking...
And air/fuel ratio does indeed affect temperature...

But in my experience, if you have proper heat range and timing, air/fuel affects it little.

I have seen plugs burn soot black rich and have a ground strap mark that is off but does not move very much when air fuel is corrected.

Changing heat range or timing will move it quite a bit though... regardless of air/fuel.


Note that two things are very important...

1- Don't just go changing heat range, because the plug is actually conducting and transferring a lot of heat. Your plug temperature will change, but so will your cylinder temp.

2- I feel more comfortable establishing heat range early, and then starting on tuning the timing. The reason is because as you advance timing, temps go up... so you can move on to a colder plug if needed... Sometimes this causes pinging you might thing is because of too much timing... The engine may make even more power with more advance and a colder plug might help you be able to get there since the plug tip temp might be the source of the ping.