NGK followed by Autolite are my preferred small engine sparkplugs. I've had a LOT of Champion sparkplugs either quit working or start hard even though the plug was clean and in good condition. I even got one out of the package missing threads once. I had used a nearly new RJ19LM to get an old chainsaw running once, (1959 McCulloch) I could never figure out why it had a weak spark, even the inline spark tester the bulb was dim, but when the sparkplug was removed and the plug wire was just jumping a gap to the cylinder it was wicked. It ran but started hard and had poor acceleration. I put a brand new Autolite in it and it started much better and I tried the inline spark tester again, it was as bright as it normally is. That was the final straw for me with champion sparkplugs. For what it's worth, the push mower my dad bought in 1977 went 23 years on the original Autolite A7N sparkplug, followed by another 12 on the SE458 (now XST458) and the standard 458 that's in it now is on it's 10th year. That engine surpassed 1000 running hours in 2004 estimating with quick math... Like it was said above, change the oil, not the sparkplug. My grandparents 1967 Montgomery wards lawn edger I inherited a few years back still has it's original Autolite sparkplug in it too, runs like a champ. The **** sparkplug outlasted both of them...