I have a Mercruiser 140 3.0L, 4 Cylinder. With a Merc carb 2 barrel. How do i adjust the carb? I took it out this pastweek to the river. The engine was kind of hard to start. i had to hold the choke flap wide open in order for it to start. When i accelerated the engine would back fire. I have to accelerate slowly in order to get up to speed. How do i adjust the carb? or is it something else? The carb was recently rebuild.