I posted this before in another thread and bares repeating:
"A good mixture will leave tan on the strap and the porcelain nearly all the way down.
Here's a plug from some one who knows what he is doing. Notice there's no timing mark? When the mixture is good it wont leave one because the mixture is homogenous and leaves a consistent colouring of the plug way down onto the porcelain. Aim for light tan. Contrary to what is perpetuated on the internet unleaded fuels tan just like leaded fuels do if the plug is white it has nothing to with the fuel type and everything to do with the mixture quality at time of ignition."
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