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89' Mariner 25 problem. Ran great, then....

D

dkf1979

New member
I have an 89' Mariner 25hp that i rebuilt the carb on, plugs, fuel filter. Today i took it to the lake and it started, idled, and ran like a top. It was pushing my like jon boat about 30 mph. After a couple hours of fishing, i started it up and and went to move to a new location. But this time when i throttled up it revved up very slowly, and max rpm was very low. I don't have a tachometer. But after the issue started it would only push the boat at about 6mph.
Any ideas? I checked spark by grounding the plugs, checked prop and it spins freely. I'm baffled! It was running prefect!
 
After a bit of research, I'm thinking I might have been running rich. I was doing quite a bit of trolling/ idling before shutting the engine off for about an hour before I experienced the problem. And I'm definitely no mechanic but I don't think my plugs with less than 2 hours run time on them should be black and oily? Maybe I'm to rich and the plugs were fouled enough from my extended trolling to prevent WOT on restart, but still capable of running at idle and starting easily? We'll research some more and do some tinkering in the morning.
 
Note that, at idling, ALL plugs run way too cold. If they didn't, they would burn up immediately at WOT.

Jeff
 
Ugh! I cleaned the plugs and tried to lean out mixture and had the same issue today. But i was hell bent on getting my 7 year old daughter to a crappie hole and decided I'd just run 6 mph all the way there. Well after about 10 minutes of running at 25% power, BAM! Everything was all good. It was running great! But then after fishing the same issue happened again! And after just running WOT at 25% it instantaneously began running great once more.
Now this evening i have the service manual out, and tested the stator and it had correct ohm readings. Then the trigger, and i get a zero reading.
Can anyone tell me if the symptoms I've described could really be from a faulty trigger?
I'd appreciate any advice!
Thanks,
Dan
Oh yeah, just trying things i pulled the top plug wire while running and the engine dried immediately. It also shocked the crap out of me so I gave up on testing the lower plug wire! Lol.. Don't know if that tells us anything. But i expected the engine to continue running on one plug, just very poorly.
 
For those that may be searching for help in the future. Flyingscott was right on. I replaced the switchbox. I also replaced the coils and plug wires just because i was ordering parts. But I'm confident the switchbox was my problem. Intermittent issues spelled electrical. Hindsight... Motor is running like a top. Thanks for your help!
 
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