The '79 Evinrude 140 on my boat has a dicey history. I bought the engine in '04 knowing the engine was blown. My local mechanic did an excellent job rebuilding it that winter and I was off to the races in '05. The engine ran pretty well but would cough & sneeze at low RPM and had a noticeable stumble until you passed 2,000 RPM. The other problem was terribly hard starting if the motor sat for a while after a long run. Once it started I would have to hold high idle for several minutes before I could accelerate with the engine bogging.
My mechanic insisted the sneeze/stumble was related to the location of my fuel tank. The boat is an 18' closed bow and the OEM tank was mounted up under the bow. Finally this year I took his advice and installed a new fuel tank in the stern of the boat. WOW,
the engine actually idled much better. Unfortunately the warm restart problem was still there.
On vacation in August (last day thankfully) I found I had a huge crack in one of the ignition coils (lower starboard cylinder). I replaced that coil but the engine was still a dog and wouldn't accelerate beyond 3,000 RPM. The mechanic looked at it and found the upper starboard coil had weak spark too. I'm thinking maybe that huge short to ground on the adjacent coil may have arced over and roasted that one. So now we have 2 new coils on the starboard and both port cylinders had the original 1979 coils. He said the old coils showed good spark, but..........they are 31 years old!!!! I had him order 2 other coils and I put those on this past weekend.
HOLY SMOKES this engine idles like it never has. Starting the motor is now just a turn of the key. Acceleration is strong and smooth through the entire RPM range. I'm beginning to wonder if this motor has had poor spark for a long time and I had just wrote that off to air in the fuel lines due to the poor location of the fuel tank.
One other thing I did this weekend was undo a dumb move I had made. The OEM foam in the motor cover was shot when I got the motor, so after the rebuild I located some 1/2" high-temp foam rubber and glued that to the inside. I wanted to get as much sound dampening as possible. The mechanic pointed out several places where the foam was resting against engine components, especially the coils and the flywheel. On Saturday I removed most of the foam so there could be air cirulation around those items. Amazingly there was no change in engine sound levels with the foam gone! Also, the warm restart problems were gone. That has me thinking the foam was causing heat buildup in the stator and/or coils which caused the hard starting. The jury is still out if that was the complete solution, but it seems to be solved for now.
KJ
My mechanic insisted the sneeze/stumble was related to the location of my fuel tank. The boat is an 18' closed bow and the OEM tank was mounted up under the bow. Finally this year I took his advice and installed a new fuel tank in the stern of the boat. WOW,
the engine actually idled much better. Unfortunately the warm restart problem was still there.On vacation in August (last day thankfully) I found I had a huge crack in one of the ignition coils (lower starboard cylinder). I replaced that coil but the engine was still a dog and wouldn't accelerate beyond 3,000 RPM. The mechanic looked at it and found the upper starboard coil had weak spark too. I'm thinking maybe that huge short to ground on the adjacent coil may have arced over and roasted that one. So now we have 2 new coils on the starboard and both port cylinders had the original 1979 coils. He said the old coils showed good spark, but..........they are 31 years old!!!! I had him order 2 other coils and I put those on this past weekend.
HOLY SMOKES this engine idles like it never has. Starting the motor is now just a turn of the key. Acceleration is strong and smooth through the entire RPM range. I'm beginning to wonder if this motor has had poor spark for a long time and I had just wrote that off to air in the fuel lines due to the poor location of the fuel tank.
One other thing I did this weekend was undo a dumb move I had made. The OEM foam in the motor cover was shot when I got the motor, so after the rebuild I located some 1/2" high-temp foam rubber and glued that to the inside. I wanted to get as much sound dampening as possible. The mechanic pointed out several places where the foam was resting against engine components, especially the coils and the flywheel. On Saturday I removed most of the foam so there could be air cirulation around those items. Amazingly there was no change in engine sound levels with the foam gone! Also, the warm restart problems were gone. That has me thinking the foam was causing heat buildup in the stator and/or coils which caused the hard starting.
The jury is still out if that was the complete solution, but it seems to be solved for now.KJ