This is an erratic problem - seems to happen after @ 30 min of running the motor, and comes & goes. I have twin '89 Evinrude 120's. The port motor looses @ 500rpms & bogs down a bit. For example, I was out over the weekend. Engines fire up fine, let them warm up, and we take off. Running fine at @ 4700rpm for @ 25 min, slow up a little to pass thru a channel, back up to 4500rpm, then it starts dropping 500rpms. It will do it for a little while, then pop back up to normal. On the ride home, it does the same thing ? loose 500rpm for 5 minutes, then back to normal, then drop off again. Ran the last 10 minutes on the 40 minute ride home with no issues at all?
I ran it the next day, on & off while drift fishing, for @ an hour, but only for maybe 15 minutes at higher rpms, and the problem never happened.
This was happening last season, and culminated in no spark to any cylinder at the end of the season. I traced the no spark to the stator, replaced it, and it fired right up. The intermittent rpm loss came right back though. Before this last trip, I cleaned all the contacts on the coils (both at the plugs and where they bolt to the block), and gapped & installed new plugs. Didn?t change anything.
It does not drop to a specified rpm either ? like it might if it was getting a temp alarm. If I am running at 4700rpm, it will drop to @ 4200, and if at 4200, it will drop to around 3700. If I throttle up, it will bring the rpm up a little, but still bogging ? I thought it might be fuel related b/c it seemed like throttling up would clear it out, but now realize it goes away sooner or later whether I throttle up or not.
The starboard motor doesn?t miss a beat. They run off the same battery, and it doesn?t matter if I am switched to the starting or house battery while running.
Any ideas on what to test, or what to inspect?
I ran it the next day, on & off while drift fishing, for @ an hour, but only for maybe 15 minutes at higher rpms, and the problem never happened.
This was happening last season, and culminated in no spark to any cylinder at the end of the season. I traced the no spark to the stator, replaced it, and it fired right up. The intermittent rpm loss came right back though. Before this last trip, I cleaned all the contacts on the coils (both at the plugs and where they bolt to the block), and gapped & installed new plugs. Didn?t change anything.
It does not drop to a specified rpm either ? like it might if it was getting a temp alarm. If I am running at 4700rpm, it will drop to @ 4200, and if at 4200, it will drop to around 3700. If I throttle up, it will bring the rpm up a little, but still bogging ? I thought it might be fuel related b/c it seemed like throttling up would clear it out, but now realize it goes away sooner or later whether I throttle up or not.
The starboard motor doesn?t miss a beat. They run off the same battery, and it doesn?t matter if I am switched to the starting or house battery while running.
Any ideas on what to test, or what to inspect?
