Got questions?

We’ve got the answers—the Summit Racing tech department tackles your automotive-related conundrums. This week, we’re reading spark plugs.

Q: I’m having a problem with my 1980 Ford 1/2-ton pickup. I put in fresh spark plugs and after 250 miles, I removed one and it was covered with black, fluffy deposits. I re-installed the plug and at 500 miles the engine began to cut out. So, I rechecked the plugs and this time they were all completely black. What is causing this and how can I fix it?

close up look at cleaning a spark plug electrode tip with fine grit sandpaper

A: Let’s do some detective workto start, install brand new spark plugs. Make sure the gap is exactly where it should be and not too wide. Next, check that you have 12 volts or more making it to the coil when the engine is running. Fully open the carburetor choke, check the float levels, and make sure the intake is sealed properly.

Then, drive the pickup for a few days and remove the plugs. If you find oil on the plugs, the valve stem seals or intake gasket is leaking and should be replaced. If black deposits are showing up again, then the carburetor is jetted too rich or valve adjustment is off. All of these factors will eventually turn your plugs black and cause your engine to cut out.

Be sure to check out our earlier post on How to Read Your Spark Plugs.

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Author: David Fuller

David Fuller is OnAllCylinders' managing editor. During his 20-year career in the auto industry, he has covered a variety of races, shows, and industry events and has authored articles for multiple magazines. He has also partnered with mainstream and trade publications on a wide range of editorial projects. In 2012, he helped establish OnAllCylinders, where he enjoys covering all facets of hot rodding and racing.