Sparkplug reading

[Anonymous]

How do you read sparkplugs? I pulled a set out of the 250 and I have never seen a brown insulator before. The center electrode and the ground electrode look great. Squared edges. The insulator is brown in color. Is this plug too hot, normal, or too cold for the engine?
Thanks,
Ken

 

[mustube]

i found some pictures off to the right of the text on this page that tell you what the spark plug reading means
http://dirtbike.off-road.com/dirtbike/a ... ?id=332655

 

[addo]

Is it a tan brown, or a rust brown? Rust colour comes from the chemical MMT, which is added to many fuels as a lead substitute.

Most plug reading articles don't mention fuel additives flavouring the centre insulator...

 

[rmt]

Brown is more or less OK. As mentioned in that article though to observe a plug for color you need to be running at a relatively high rpm for a sustained period (at least a few miles worth), shut down as quickly as possible and then look at the plug. I usually turn the ignition off and coast to a safe place to pull the plug.

 

[Anonymous]

You hit it addo, the color is dark rust brown. I have heard about the additives, but know nothing about them.
Thanks for all the help,
Ken

 

[addo]

Glad I could help. The first time it happened to me, I freaked right out - thought the bores had corroded! FWIW, I have spoken to an additive manufacturer locally, and they conceded the public should be advised of this appearance change.

The lack of lead in modern fuel renders many of the old "colour codings" redundant. The Gunston's kit with a special plug that has a clear insulator to see the flame colour, is still of some use when tuning.

Regards, Adam.