The smoke came from the board.
Look at the picture, the fet has drooped as the solder melted. As I said, this is a standard ELF. It would have passed production test, but as soon as it was under load it blew. I'd say it was a faulty fet. Just one of those things.....

Incidentally the tank was running chassis only, and had only just been switched on so no there couldn't have been any overheating. I will fit a fan, but I'm hoping that the fan conversion to the smoker will provide enough air movement.

Can't comment yet about the difference in speed. The Bulldog is S&S, and the Pershing is either non S&S or one tracked S&S....

Jo