Hayes COLORTUNE Fuel System Tool - 12mm & 14mm Spark Plug Tool - Ships from USA

I have used Guson Colortune for years. I use this for LBC MGB 4 clinder cars. I think the results are good, but can be subjective when comparing colors.

You use it to help gauge air fuel mixture but the one I received misfires about half the time, causing the cylinder to load with fuel. Which makes it impossible to use for the intended purpose.