I have an 89 2.3l omc. It idles great but bogs down about half throttle. I know what the problem is, I just don't know how to fix it. once the engine is warmed up the choke is wide open, as it should be. Right? as soon as i throttle up about half throttle the choke starts to cloce again and the engine bogs. if I have someone hold the choke open while i throttle up it runs great. What could be causing this and how can I fix it.