Reply #48: I just re-built my ten-year old lawnmower last week.

[Ikonoklast]

It stopped abruptly after about five minutes running, in a puff of blue smoke and some rather loud metal-on-metal noises.

I popped the head off, and saw that the valve seats were covered with carbon and they weren't closing all the way, preventing proper compression and fuel combustion. I scraped the excess carbon off the vavles and the head, cleaned the intake up real nice and put it all back together.

Started on the first pull, and ran even quieter than before.

But, then again, this is a simple side-valve single cylinder four-stroke motor with no electronic components to fail. A fairly basic mechanical fix.