One (or tow) cylinders cutting out

'93 Merc115 erratically cuts out and back in at idle, full throttle, or any where else, under load or not, hot or cold. It's like it drops a cylinder or two briefly. Seemed to get better through the season (this is the 3rd season it has done it) but not too sure it does. Figured it was burning through varnish or crap in the gas but continues tank after tank. Just went through the carbs and were perfectly clean. Changed the filter, have an in-line filter/separator, treat gas off season, ran SeaFoam through it, plugs are perfectly clean. Used engine tester/tach inductance pick-up to check each wire. Would expect when cutting out would get no rpm's indicated on one wire, instead each shows slowing down as engine does but always something.

Would really like to avoid the automatic $800 charge for carb rebuild whether it needs it or not and do without my boat for 4 weeks if I take it to the dealer. Any suggestions what to check for?

Re: One (or tow) cylinders cutting out

Check the trigger wires for deterioration it sounds like a trigger problem here's a test for the ign system