I have a 04 exmark 36" with a 15 Kohler motor on it. Is not that easy to start I do not know why, but once I start it; right away it spits gas out of the exhaust. But then it stops. I have no clue what it is I thought it might be the valves but if it was the valves it would keep spitting gas out. ..... I am lost on this one I have no clue what it is. Any help? Carb probs?