1985 mercury 150 issues

[Celler555]

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!

[faztbullet]

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

[Celler555]

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

Thank you so much. Ill use this info tomorrow in troubleshooting. Hopefully it’s not a bad stator!

[timguy]

Welcome. Test trigger IN ALL THROTTLE POSITIONS. Why? A wire may be loosing continuity at more advanced timing positions, hence the "bogging".

[Celler555]

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

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?

[faztbullet]

Should be just fine...

[Celler555]

Should be just fine...

much appreciated for the help!

[timguy]

Pappy, can the rectifier get hotter?

[faztbullet]

Same 4 bridge rectifier is used on 9 and 16amp stators...

[timguy]

Excellent, thanks.