[Kurt in NJ]

I used to play different spark plugs, would only put the 3X ones in for shows--- then about 30 years ago I left them in, got better fuel mileage and ran better, still using same ones, amortized over 30 years they are cheap

Most likely the original poster has a mixture problem, I have no problem burning the 3x white when I set mixture lean--- I did testing with emissions machine under load to know what gav setting gives good mixture on my car