andyr
Member
Boat yard installed a factory Mercruiser long block 5.7 roller lifters, non vortec. On the test run it backfired occasionally, required more throttle than the starboard engine, seemed to vibrate, not feel right. Put a carb kit in. Ran engine 12 hours various rpms up to 3200. Eventually, couldn't run over 1800 rpm without backfiring repeatedly but would rev up fine in neutral. I found all the the plug wires are reversed. Left side on right etc. Is this new engine damaged as a result? Since the backfiring got worse, was something getting damaged. Valves? What would you do?