Moin Moin, my STIGA seat mower, 12.5 hp, bend handlebar, built in 2002 with mulch mower runs like a 1. Every year maintenance, oil change, candle etc. My problem is this after the mow, when I put the mower out, about 2 seconds after the parking by key, there is a last combustion. There comes then a very loud bang out of the exhaust, partly also a flame. But it is only a bang! It also doesn’t matter if I put it off right after the mow or if I put it down a little bit with lower What can that be? Greeting Sven