I have had intermittent problems with my 15 hp mercury. It is getting worse. When I run wot for a period of 40 minutes or so it cuts out and stutters. It isn't fuel because it starts right up. I have replaced all fuel lines, filter and cleaned the carb! The engine is not overheating, a new impeller this season I suspect a coil going bad. I took resistance readings. across the brown and black (primary) I get .3 ohms??? across the two spark leads I 4.7k primary is supposed to be between 16 and 24 ohms. The secondary should be 39 to 50K ohms. The resistance boots read 4.7k I get no connection to the metal pole piece that grounds it to the block?? It seem funny that this failed at less than 300 hours. The spark is reddish orange, not blue even at night. To test it further I gaped the plugs at.040 inches and the engine just missed a bit, not the total cut out but not smooth like .035 inches. I have read posts all over about coil and weak spark issues. Has Mercury had a redesign on this? How do I know I get the revised one. Motor SN OT987569 It is difficult to bring this to a shop for repair because I can run for two or three days without problems. After a restart it may be fine.
