I don't run cars but have helped those that do a few times. Dirt and lean runs seem to be the killers on these little screamers. Just because it has an air cleaner (most are fairly crude) doesn't mean some dirt isn't getting thru. Like anything else the air cleaner
must be serviced often or it will restrict and change needle settings as it clogs up. Most cars seem to be owned by those who demand the highest rpms at all times, thus starting out on the lean side.
That combination will kill any engine large or small.
I have owned large Bull Dozers that required air cleaner service every day and the dirt collected was in the pounds, some of the small model off-road vehicles are operating in about the same conditions with a little foamy "air cleaner" that I wouldn't consider using on
anything I valued.[:@]