The motor is a 1994 Mercury 4IL electronic ignition carbureted 115HP.<br />I was running at about 2800-3000 rpm when the motor shut down like I pulled the throttle back.<br />I tilted it up and checked the prop for damage and found none.<br />I cranked it and it started it right up, but it was making a slapping metallic noise at idle.<br />I carefully advanced the throttle and the noise went away.<br />I ran it back home at lowest speed to keep on plane and the engine sounded and operated normally.<br />I listened all over it and could not localize the noise, but it was a definite metallic slapping sound.<br />I pulled the boat - had to run it over to the ramp about 3 miles, again sounded normal at low speed plane.<br />In the driveway with the flushette on, can barely hear the noise over the exhaust, but can hear it as engine coasts down if turned off at about 2000 rpm.<br />Pulled the exhaust cover and #4 piston is scored on the near side. Cylinder walls have minor scoring on the opposite side (can't see the near side) obscuring the cross hatch pattern visible in the other cylinders.<br />Compression is 145-150 in #1, #2, #3 but 87 in #4.<br /><br />Got the power head ready to pull. Will check the cylinder for wear and try honing it first, then maybe get it bored for OS piston.<br />Looking for help on what might have happened.<br /><br />Engine seems to be getting plenty oil, maybe even too much. Lots of blue smoke at idle and when I checked the oil injection pump setting it looks like it is set a little rich.<br />This engine does not have idle jets in #3, #4 carbs. I wonder if it gets enough lube in those cylinders at low speeds.<br />It is also bad about lag coming out of the hole, particularly the first time after no use for a while.<br />I'm thinking about buying new carb bodies for #3 and #4 like #1 and #2 that have idle jets, but using the #3, #4 main jets.<br /><br />Any ideas about what to look for as the cause of the problem and whether the carb change is a good idea?<br /><br />Thanks,<br /><br />Al
