Name:   CAT BOAT - Subject:   225 Merc OB surging Date:   10/30/2014 3:43:52 PM (updated 10/30/2014 4:00:01 PM)

Merc Optimax is my favorite engine.  They are intesting machines.  They are both fuel injected and air injected engines.  Your problem is most likely on the FUEL side.  Optimax has a low pressure pump/lift pump and High Pressure fuel pump and they must be serviced properly.  Optimax is a DI (direct injection) engine, meaning the fuel/air mixture is injected directly into the cylinder while under compression.  Any drop in fuel pressure less than 38 psi AT THE HIGH PRESSURE PUMP will result in a lean condition/surge.  Do not operate the engine with this concern.  You will certainly damage the powerhead.  It is possible that the "Air Pump" (belt driven from the flywheel) is weak, or in need of service but not likely. Some early models were not serviceable.   If your previous shop/mechanic did proper maintanance and had the right equipment he would have done it already and then that prolly is not the trouble.   We have a computor program we run through the engine that will test the injectors and point out any problems and can certainly let you know what is wrong.  Another thing that may be causing the surge is the "high pressure pump screen" in the VST (Vapor Separation Tank) in the fuel system....  But, has it ever been serviced?  Mercury Optimax is a very complex engine.  They make a lot of power, sip fuel and still pass EPA standards as a 2 stroke.  Sorry for the long post/reply.  We will be happy to help you.  All that being said, the boat would need to be at our shop to diagnose and repair.  I am an hour away from you!!!  If you don't drive here, make sure you land at a Marine facility with the proper equipment and knowledge.  Also, there are a few other minor items that can cause your problems.

Respectfully,

Steve Northington

Cathouse Marine, LLC

334-358-2838