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1985 mercury 150 issues

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Celler555

New member
Hello all, I hope I have posted in the correct forum as I am new to this website. I have a 1985 mercury 150 serial: 0a138816 that I got a week ago with a known issue from the previous owner where it bogs down and sometimes dies if you don’t let off the throttle. I started diagnosing fuel issues first but could not find anything wrong with the fuel system (even rebuilt the fuel pump because that was my one thought in my mind) I started testing ignition next and found out my motor is only running on one bank of cylinders (135). (246) are not firing. I have compression tested, have replaced plugs, switch packs, and have ohm tested trigger and stator and they are within specs according to my manual for the engine. I am at a complete loss and would greatly appreciate any help on what I need to check/replace as my local marine mechanic (azle, tx) cannot get my boat in for a few weeks. Thanks in advance!
 
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Only 3 things will cause this: 1) stator down on one side. 2) switchbox bad. 3) blk/yellow on pack not firing pinched/shorted to ground. You in luck as this is easy testing...1) swap red/blue wire on switchboxes, if problem moves stator bad. 2) swap boxes if problem moves box bad, only replace as a pair and use only OEM, Serria,ProMarine and lastly CDI. 3) Blk/yellow can be pinched between boxes as it splits from single wire in harness above them
 
faztbullet said:
Only 3 things will cause this: 1) stator down on one side. 2) switchbox bad. 3) blk/yellow on pack not firing pinched/shorted to ground. You in luck as this is easy testing...1) swap red/blue wire on switchboxes, if problem moves stator bad. 2) swap boxes if problem moves box bad, only replace as a pair and use only OEM, Serria,ProMarine and lastly CDI. 3) Blk/yellow can be pinched between boxes as it splits from single wire in harness above them
Click to expand...


Thank you so much. Ill use this info tomorrow in troubleshooting. Hopefully it’s not a bad stator!
 
Welcome. Test trigger IN ALL THROTTLE POSITIONS. Why? A wire may be loosing continuity at more advanced timing positions, hence the "bogging".
 
faztbullet said:
Only 3 things will cause this: 1) stator down on one side. 2) switchbox bad. 3) blk/yellow on pack not firing pinched/shorted to ground. You in luck as this is easy testing...1) swap red/blue wire on switchboxes, if problem moves stator bad. 2) swap boxes if problem moves box bad, only replace as a pair and use only OEM, Serria,ProMarine and lastly CDI. 3) Blk/yellow can be pinched between boxes as it splits from single wire in harness above them
Click to expand...

I switched those wires around you said to and the problem moved. So it is my stator. Is it possible to run an higher amp stator on these engines? I found one through CDI that is a 15 amp vs the 9 amp it calls for. Im running some big electronics on my boat and if possible I’d like to upgrade the stator to the 15 amp I found. Is this possible or will I burn up my rectifier/battery?
 
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