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Losing fire on center cylinder

D

darkhorse

New member
I have a 90 HP Merc Mariner outboard that keeps losing fire on the center cylinder. Has anyone had similar problems and perhaps know the cause?
 
Intermittent, weak, or no spark at any one spark plug usually indicates a bad SPARK PLUG, COIL, or SWITCH BOX. Per CDI.
 
Yes, I changed the plug and the coil, but still have intermittent spark on that cylinder. Any help would be appreciated. Thanks
 
a good freind just had same prob with a 90hp merc jet set up. drove him peanut zy. it turned out to be what john/evin calls a timer base. its a trigger coil (3 one per) that tells the cdi when to fire. it was on/off for a long time we caught it on a off time. we ohmed out the three and one was way out. cheapest part of the whole cdi to replace. after getting mad so many times he is now happy. its a quick and easy check. my $.02
 
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