1989 115 Help?

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My dad recently passed and the last time he had his boat out, in the fall he was having issues with it getting on pad. I'm going to need to sale it to help payoff some bills so looking to see if I can fix it. He said it started and idle fine, when trying to put in on plane it would only turn about 2500 RPM's. He could put it in neutral and rev the motor to 3500-4K and it sounded good/strong. I know the injectors have been by-passed and he mixed his own oil. If you have any suggestion on what to look at would be very much appreciated.

Thank you!

[JOE54]

ser num would help ,check basics first compression ,spark on all cyl, fuel system integrity

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Update: Took it to the lake and it will not go over about 1800 RPM’s. Starts and idles just fine. Got home and checked not getting spark to 3&4, swapped out the coil wires from 1&2 to 3&4 and get spark. This is a “2+2” motor from what I’m reading. So should all the plugs get spark? My understanding is it only starts and runs up to 1800 RPM’s on 2 cylinders.

[JOE54]

stator or sw box , you can swap leads for stator to determine if its good, betting on sw box

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Okay not a outboard mechanic so this looks to be my wiring diagram, “colors” looks correct. Just swap both red/blue wires from the stator? https://maxrules.com/oldmercs/Wiring/1966ona/60.jpg
Then if the problem moves stator problem? Could the trigger cause the same problem? Thank you so much for your help!

[JOE54]

yes just swap wires reds and blues /could but doutfull its trigger

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Thanks Joe for all your help! Replaced the switch box, picked up a used OEM off eBay cheap. Installed it after work and took the wife to the lake for a test run. It ran great, just wish dad was here to enjoy his old boat again.

[JOE54]

job well done