77' 140 cuts out above 3,000 RPM

[77Cobia]

Recently purchased a 77 Cobia with a 77' Johnson 140 (first boat). Had it on the river for the first time and she ran great for the first half hour. After that she suddenly started to cut out and stalled. Got her re-fired and started to do the same thing but only when I pushed her over 3,000 RPM. Started by pulling plugs and the top right cylinder was black and wet. I then noticed that coil pack doesn?t match the others and the wire was starting to back out of the pack. Pulled on it and it came right out, the wire was green and corroded. So I assume that cylinder was not firing due to the bad wire and that?s why that plug is fouled and black.

My question is, would this cause it to run ok below 3,000 and not above?? Seems to me I should have heard the miss and felt it all through the RPM range. My initial though was fuel delivery but seems that would be felt all through the RPM range?. I have been under the hood of many cars but this is my first outboard so I am hoping to learn here?


Also i cant find a Gap setting anywhere for the plugs..

 

[ezeke]

Re: 77' 140 cuts out above 3,000 RPM

Probably for the reason that the listed spark plugs are surface gap with nothing to set. If you choose to use the QL77JC4, the gap would be .030.

http://www.boatsetup.com/Spark Plug Chart 2007 BRP.pdf

http://continuouswave.com/whaler/reference/BRP_SparkPlugChart2007.pdf

The motor is probably running on three cylinders because of your coil and wire. You should replace any ignition coil that shows damage: cracking, melting or discoloration. The wires must be solid core and perfectly seated to work correctly. The ignition coils should be black if they are OEM, not green.

 

[77Cobia]

Re: 77' 140 cuts out above 3,000 RPM

My local johnson dealer recomended i use the original no gap plus for the motor. is there really that much difference? I also found that the coil packs had been replaced with the new style packs so i am going to replace all 4 back to original... thanks for the help ill let you know how things turn out this weekend.