1987 4.3L Mercruiser -- Last year on water burnt a hole in #2 piston. Pulled engine (rings, bearings, one piston, timing set, oil pump, cap, rotor, wires & fuel filter). Timing was set at 8 degrees. When in water, from a dead stop you can push throttle wide open and boat will plane out well and run fine until about 3500rpm. However, boat will plane out well at 1/2 throttle until 4-barrel opens, then it begins backfiring and missing (like the valves are trying to float?). When I pull it back to 1/2 throttle it runs just fine. When the backfiring and missing are occuring and I adjust the trim, the motor almost dies.
