I need some help with my 1996 60 HP Johnson 2 stroke outboard (Model Number J60TLEDR) with ~ 500 hours on it.
The problem I'm currently experiencing is an intermittent misfire/stumble that occurs noticeably from idle RPM at least up into the upper mid-range, once the engine warms up; it *seems* to run a bit better when stone-cold, at least for a minute or two.
In the process of diagnosing this problem, I have:
This morning, when using the timing light to recheck idle timing, I noticed that if I left the light on for a few seconds, the light flashes were occasionally -- and irregularly -- interrupted for what felt like from one cycle to a few cycles. The missing flashes coincided with a slight engine stumble. Increasing the RPM (by simply rotating the connected throttle linkages right at the carbs) showed that the misfiring tracks RPM, as close as I can tell. To my surprise, the missing flashes were the same for the other two cylinders; I was not able to detect any differences between the three as I
moved the timing light between spark plug wires.
The fact that the misfire is the same on all three cylinders, and that the power pack has been replaced to no effect, suggests (to my rudimentary understanding of this ignition system) that it's something feeding the power pack an erroneous signal for all three cylinders. The three candidates that come to mind are the stator, the timer base and the magnets in the flywheel. It's hard to imagine much going wrong with the magnets, but I can see the stator or the timer base being a problem; is one a much more likely failure candidate than the other? And do the symptoms I describe (or some other test I can run ...) suggest one or the other?
Does anyone have any suggestions as to how I should proceed?
Thank you in advance for any help offered.
The problem I'm currently experiencing is an intermittent misfire/stumble that occurs noticeably from idle RPM at least up into the upper mid-range, once the engine warms up; it *seems* to run a bit better when stone-cold, at least for a minute or two.
In the process of diagnosing this problem, I have:
- Replaced the power pack (which made no difference in this symptom),
- Checked the static resistances of the three ignition coils and the spark plug wires (all OK),
- Completed the "link & sync" procedure according to the manual (no difference), and
- Replaced the spark plugs (no difference).
This morning, when using the timing light to recheck idle timing, I noticed that if I left the light on for a few seconds, the light flashes were occasionally -- and irregularly -- interrupted for what felt like from one cycle to a few cycles. The missing flashes coincided with a slight engine stumble. Increasing the RPM (by simply rotating the connected throttle linkages right at the carbs) showed that the misfiring tracks RPM, as close as I can tell. To my surprise, the missing flashes were the same for the other two cylinders; I was not able to detect any differences between the three as I
moved the timing light between spark plug wires.
The fact that the misfire is the same on all three cylinders, and that the power pack has been replaced to no effect, suggests (to my rudimentary understanding of this ignition system) that it's something feeding the power pack an erroneous signal for all three cylinders. The three candidates that come to mind are the stator, the timer base and the magnets in the flywheel. It's hard to imagine much going wrong with the magnets, but I can see the stator or the timer base being a problem; is one a much more likely failure candidate than the other? And do the symptoms I describe (or some other test I can run ...) suggest one or the other?
Does anyone have any suggestions as to how I should proceed?
Thank you in advance for any help offered.