I've got the same machine with the 25HP Kawi. When I first got it, I would pretty much go from full throttle, to idle than off in a couple of seconds after mowing. It would then backfire a second or so afterwards. I never thought about it, but members here mentioned letting the engine idle for a minute before shutting down, to let things cool, and allowing the engine to catch up to the throttle. Makes sense to me, I can see where going from full throttle to idle than off, could allow some unburnt fuel out the exhaust, then ignite in a hot muffler. It never backfires now that I idle for a minute before shutting down. As far as starting, she fires right up with choke, never a problem, love this engine.