help with mid 80s mercury 75hp

nhboat

Cadet
Joined
Jul 23, 2017
Messages
13
hi, i just bought a boat with an 84-86 mercury 75hp 4 cyl. it skips and pops some when it runs with muffs on. dont want to try it in the water until it runs much smoother. i was told the coils, and pcm were replaced. compression is about 130 all 4 cylinders. new plugs. i checked wiring and found some corrosion and weak wires. 2 went to the trigger so i ordered a new trigger and merc flywheel puller since a normal puller hasnt been able to budge it. do you think the trigger is the likely cause to it stumbling and rough idle? it starts with a little diffuculty, and then will idle all day but def stumbles and skips. give it gas and it sounds alright. when i pulled the plugs out, #1 had some black deposits that looked normal and #2,3,4 still looked brand new but were just wet with gas. no black carbon deposits on it. still looked brand new as if they werent firing. im new to outboards so any info will be great!
thank you! im in nh btw and if anyone is close that knows these engines esp when it comes to the timing, i could really use the help. ive been reading and watching youtube but it still seems so foreign to me when it comes to setting the timing.
 

UKMike

Seaman
Joined
Apr 15, 2015
Messages
55
can you put a movie of it running on here? that will help everyone understand how bad and what it could be.
 

nhboat

Cadet
Joined
Jul 23, 2017
Messages
13
ok i can try that once i get it back together. i have things apart right now to replace the trigger once that comes in. if its still running rough after the trigger replacement i will post a video.
 

UKMike

Seaman
Joined
Apr 15, 2015
Messages
55
OK, I had the same with mine and ended up replacing the trigger and stator and that did the trick, I don't know which was at fault but it worked, that was after replacing the ignition modules though and I should have replaced the trigger first.
 

nhboat

Cadet
Joined
Jul 23, 2017
Messages
13
well its good to know im on the right track... maybe.
my dad found on badly corroded wire and although it felt like it was still connected it looked green and very thin. so we cut it back to splice in a new piece and it just kept crumbing in my hands so i thought id start with the trigger. i almost bought a stator too but figured its easy to replace without to much dissassembly. did you have to buy the merc flywheel puller? ive tried to use a normal puller to get it off and its not budging at all. it actually broke the puller in half. so i ordered the merc tool. i hope its not permanently frozen on there. its soaking in oil and ive also tried a little heat
 
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