I have a 1998 225hp ox66 SWSII, Shortly after I got the boat the engine made a hole in a piston so I replaced the piston, all rings, thermostats and gaskets and the machine shop installed a new cillinder sleeve. After restarting I replaced the water pump, o2 sensor, VTS filter, spark plug caps, engine filter, fuel water separator, spark plugs, the three low pressure pumps, and messured high pressure fuel at 35psi constant. the engine has a very rough idle and rough running below 3000 rpm. On accelaration it stumbles until around 2900-3100 rpm when it jumps to 3400 rpm and seems to run fine at high rpms. Also the engine surges 200 rpms up and down at around 3600 rpm in rough seas. The engine wasn't reaching 5500 rpm only around 5200-5300 rpms so I used a smaller prop and then the engine surges rapidly at around 5200 rpms. Any suggestions??
