Hey Blumby, watched your video, that wasnt too bad, ive had them spewing white smoke for up to 5-6 minutes at times. It cleaned up really nice though. Pity the person you sold it to was a nuffy.
On a side note, it sounds like its revving too hard, the other giveaway its overrevving is the spinning front left wheel. Back the revs off a little or someone will blow it up and then tell you that you sold them a dodgy mower.
They are pretty popular units, finding another buyer won't be a problem.
Cheers, Theo