The 3gm30 in my 1990 C&C 34+ runs great when running, but when cold has a tough time getting going. I have to give it a lot of throttle and 3-4 full seconds of cranking to get it started and then is sputters for a bit with plenty of blue smoke before it settles in. Any ideas as to whats up?
First thing I would check is the mixing elbow. The elbow on our 2gmF was almost completely blocked, which made for very difficult starting. The exhaust blockage was just before the water inlet, so the water was still flowing freely out the back of the boat.