Not with standing that there may have been an assembly mistake on a single shift , four mowers catching fire out of 25,000 is no proof of a design flaw.
There are only 4 people who have responded to this thread with a burned mower over 4 years so it is obviously not a daily occurance
mowers catch fire usually because of a build up of debris around the muffler & / or exhaust pipe .
Mower manuals tell owners to check & clean debris from their mowers after every use,,,,, no one ( me included ) ever does.
It is becoming much more common as engines are running a lot leaner, thus a lot hotter.
So you have dry hot grass clippings being fanned by the hot breeze off the engine.
Remember starting a fire by blowing on smouldering grass when you were camping as a kid ?
I see about 5 or 6 mower fires a year, always either at the very beginning ( mouse nests ) or during a hot dry spell ( clipping build up ) .
A cheap car fire extinguisher clipped to the rear guard is a regular recommendation & I have fitted dozens of them to the mowers used by my elderly customers .
It takes near 15 minutes for a 1/4 fuel line to burn through and the smell of burning neoprene ( outer cover ) or N-Bunya ( inner tube ) rubber is very pungent and can be smelled for blocks
However the smell of burning HDPE or PVA is no where near as obvious and both can be set alight with a match where as fuel lines need a lot more heat .
As for being a design flaw , more like a cost cutting exercise.
Quality mowers like JD put vents in the top of the hood and ducting to go between it and the blower housing so the mowers cooling fan is sucking the cleanest air to blow over the engine thus limiting the possibility of debris build up on the engine.
This adds about $ 10 that no one seems to be willing to pay top the cost of the mower so it is not a regular feature on most new mowers.
