Are plug cuts valid with unleaded?


New Member
Mar 31, 2005
Columbia, SC
I have read that using a plug cut to estimate mixture does not work with unleaded. Any valididity to that? If so, what else can one do short of an 02 sensor and guage? I am working on my jetting and want to make sure I am not too lean.

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what the heck are plug cuts? reading plugs is standard practise regardless of fuel choice. gasoline, leaded or unleaded reads differently than alcohol or alcohol/nitro, or propane, but all fuels leave a deposit on the plug when burned.
If I understand correctly, a plug cut is driving along at a certain rpm, then shutting the motor off without taking your foot off the gas and coasting to a stop to pull and read plugs. What you see is what the mixture is at that rpm. Still valid with unlead fuel. Rich is rich and lean is lean. Short of putting in a wide band O2 sensor, this is a valid method; a bit better than driving the car to a stop, then pulling and reading, which is reading a mixture at idle.