I don't have any small engine equipment that's 25 years old (though my chain saw is getting there), but yeah, 4 strokes shouldn't need plugs very often. 2 strokes, well maybe a different story.I don't know why they came up with this change spark plugs every year. you don't do it in your car, why does a small machine need it. Some of my machines are 25 years old on the original plugs..
I've heard that, but no one's ever elaborated. Is it that they have a higher center of gravity than, say a lawn tractor making them tippy or is it a traction issue?Keep in mind that Z-turns have issues with hills. Is your yard more or less level ?
As far as box store mower vs one from a power equipment dealer, much depends on your age and how much use it'll get. I've had decent enough luck with box store mowers in the past, not sure a pro model is worth the extra money for a homeowner.