The "leak" Might be fuel blowing out of the muffler as he try to start the engine (i have this all the time, flooded engine, ~5 flips past fuel to carb, then turn and out comes fuel), but he dose need to check for a fuel leak else where. As to how fast you need to flip it, because it is a small 2 stroke you only need to quickly flip the prop past TDC. Quickly for me is ~25% of my strength into the prop (I'm kind of small, and have seen my engine started with just the flip of the fingers on the spinner!)