I recently purchased my 757 and have two questions. First off, at what throttle% do you engage your blades? Full or barely on? I've heard it's bad for the machine to do it at full throttle, but at low it almost stalls the engine. Also, when the machine shuts off every time I get a backfire. I know what causes this but is it normal for a new machine or does the carb need some adjusting? Thanks in advance.