I have a 1988 OMC 5.7L 260 HP engine and while taking it out for the first time this weekend it would stall when i put it into gear. It wouldn't happen every time but maybe 50% of the time. Also, While we were out it sounded like the engine back fired and after it would only give me half the horse power and the engine sounded slightly louder. Any idea what the problem may be? Thanks!