I have a 1986 Johnson 140 BJ140TLCDC. It starts easily at first but has an intermittent fault, which makes it run very roughly. No real pattern to the firing sequence as if it is running on 1 cylinder with the engine jerking all over the place as it appears to stall but then kicks back to life. I have cleaned and rebuilt the carbs, bought new plugs and ensure the plug leads were not earthing, all was fine. I then purchased a timing gun as I thought it maybe the coils. I was expecting the engine to be running roughly with the gun not flashing when attached to the ignition lead for the coil on the cylinder not firing. This was not the case, all leads flashed in time to the engine kicking back to life, as if each cylinder would miss a few beats then take a turn at firing (so the light on the gun for every lead was erratic but in tune to the engine). There was no constant ignition sequence, indicating fuel starvation as the route cause (good spark but no combustion in the chamber). In summary I have an engine that fires on all cylinders it simple misses a few beats here and there and this issue is on all 4 cylinders. The engine sometimes dies and will not start again unless left for some time, or will stop spluttering and run normal and when it does run it runs great. If it is running properly (post its coughing and spluttering phase) it runs great, however you cannot tell when it will die again, it could be 20mins or it could be 1hrs or just keep running. That said on every start-up it goes through a rough patch at some point and then it may work or may not.
I was thinking about replacing the power pack, but I do not want to waste money if this is not the issue as it could equally be something else like the Timer Base & Sensor assembly or something I have not thought about. If I do a static test all checks out great, however as soon as the engine is running there is this issue. I am a newbie to boating so if I have not used the correct terminology, please go easy on me. That said I do need your expert help so however it is fed back is more than welcomed.
I was thinking about replacing the power pack, but I do not want to waste money if this is not the issue as it could equally be something else like the Timer Base & Sensor assembly or something I have not thought about. If I do a static test all checks out great, however as soon as the engine is running there is this issue. I am a newbie to boating so if I have not used the correct terminology, please go easy on me. That said I do need your expert help so however it is fed back is more than welcomed.