merc 225 rough running

My 94 225 was running really well up until three days ago. It feels like it is not hitting on all cylinders. I have comp tested it, changed plugs, drained the carbs..still runs the same. I checked for spark on all plug wires and they seem ok. Once in a while when driving the boat it will start hitting on all 6 and take off...but other than that it runs like crap. The foam insulation in the motor cover started falling off and it looks like the alternator/flywheel made a real fine foam mist out of it...wonder if the carbs sucked any of this in? Or maybe a reed problem? Thanx...

Re: merc 225 rough running

Carbs probably sucked some in. Probably didn't do any harm. I'd bet on an ignition problem. If you connect an inductive pickup timing light, it'll stop flashing when the cylinder stops firing. You can test each cylinder this way while running it next time.

Re: merc 225 rough running

Like Willy said check it when running it and make it act up. When it does act up I would check the spark by using a timing light just like Willy said. If you notice that one bank of cylinders are not firing such as 1,3,5 or 2,4,6 then I would say you need a stator. If you find out that yes in fact one side of the motor is not firing at all when it acts up then find your stator wires and you should see 2 blues, 2 reds, 2 yellows. You can take the same color wires and switch them with the other same color wire. Do that with the 2 blues, 2 yellows, 2 reds. Once you swap the wires with the same color then test the boat again. Lets say the first time you checked it and found 1,3,5 not firing and after you switched the wires around you found that 2,4,6 are now not firing. That would mean that most likely you have a bad stator. If you noticed that both times of switching the wires that it made no difference and that 1,3,5 are still not firing then I would say you need a switchbox.

Re: merc 225 rough running

update...I took it into the shop here and they ****ed around with it..put new plugs in it, etc. All seemed well and they asked me to come in to see/hear it run in the tank. I went there and it sounded good and seemed to run strong. Took it to the lake that nite and it still pulled like a dog. Next morning I went thru it again myself and found that number 6 cylinder had no spark. Took coil outta number 4 and hooked it into number 6 wiring harness and had good spark. Took the coil down the their shop and they confirmed it was bad....new part will be in tomorrow..keeping my fingers crossed. thanx to all that replied...john