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uh oh, motor trouble

1979checkmate

1979checkmate

Member
1979 merc 115 TOP. was out a couple hours last night, boat running awesome, but i was pulling up a skiier and the motor just quit. had zero power could not go over an idle and sounded rough. When i {finally} got home i imediately did a compression test and all cylinder checked out good (130-135 psi). so i cranked her back up and she ran rough again, with a thick pume of smoke coming out the exhaust. (so thick it hugged the ground instead of going up. To me this seams like unburnt fuel so a spark problem? im going to replace the plugs today just to do the easy stuff (they were replaced at the beginning of the season). but what else do you guys think this could be? Stator or switchbox(s)?
 
I wouldn't replace the plugs yet, especially if you replaced once this season already. Considering it was running terrible and the rings/cylinders/pistons don't seem affected, I would start with checking for good spark on all six. You should find your way to the problem from there working in.
 
Would it hurt anything to remove and unplug all spark plugs and test each cylinder one at a time with all spark plugs remmed so it doesn't fire.'or should i leave everything connected and run the motor while checking spark one at a time.
 
number 2 cylinder has no spark. so i am assuming that ignition coil is bad? if it was the trigger coil, stator, or switchbox wouldnt it cause more than just 1 cylinder to have bad fire. Also, could no spark on just 1 cylinder make the performance this poor?
 
okay i ran a test on that iginition coil and it checks out fine. i swapped some spark plugs around and fired it up, this time at the begining of the test it still had no spark, but a few seconds in in started sparking and the motor ran great! took the tester off hooked it back up and tested again. Once again, ran like crap a few seconds and then it started sparking and ran great? What would cause this sparatic working and not working? switchbox? just replace plugs?
 
You may want to check all the connections and wires to the coil or you could have bad plug wires . I would check those before you replace anything. That would explain the intemitent spark. usually if a coil is bad, its bad not just malfuntioning once in a while.
 
Inspect the coil for cracks, check and clean the connections. Did you check all the leads for cracks in the isulation? It don't think its a switchbox if its only on one cylinder. Check each lead for continuity.
 
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