mid 1990s mercury 75 problems

Ed27518

Cadet
Joined
Oct 12, 2019
Messages
15
Hey guys, I have been having some odd problems with my mercury since I bought it. It looks really clean under the cowling and has 130 lb compression on every cylinder. When I bought it I did not know the running condition. I rebuilt the carbs, put new fuel lines on it, new oil lines, cleaned oil tank, new impeller. This is where it gets complicated. At first it would not run. Then one day I decided to try to start it and it randomly started and ran great. Then it would not start the next time I tried. We even sprayed starter fluid in the carbs directly without the airbox (i know its not always a good idea but I only do it sometimes). Tested spark and had spark on all cylinders, although it did seem a bit intermittent. Then It eventually decided to start again one day. Ran rough. For a while I could get it to start and I would troll to fishing spots with it, but it would shut off and not want to start again for a while. Then I took it out and gunned it, it proceeded to plane out and run great at high speed, got a couple miles down the lake and throttled down slowly and it cut off and wouldn't start again. Now I can get it to run barely but it likes to shut off unless the throttle is advanced and it sounds bad. I am almost certain it must be the stator/trigger. What do y'all think? (yes I tested compression after all of this and was still 130 on each) (I also retested spark and saw spark on all three)
 

CaptnKingfisher

Petty Officer 1st Class
Joined
May 14, 2017
Messages
259
Sounds like a failing ignition circuit component, bad ground or loose wire. Get a manual and methodically check everything on the circuit
 

GilLesS72

Cadet
Joined
Apr 29, 2021
Messages
18
Hey guys, I have been having some odd problems with my mercury since I bought it. It looks really clean under the cowling and has 130 lb compression on every cylinder. When I bought it I did not know the running condition. I rebuilt the carbs, put new fuel lines on it, new oil lines, cleaned oil tank, new impeller. This is where it gets complicated. At first it would not run. Then one day I decided to try to start it and it randomly started and ran great. Then it would not start the next time I tried. We even sprayed starter fluid in the carbs directly without the airbox (i know its not always a good idea but I only do it sometimes). Tested spark and had spark on all cylinders, although it did seem a bit intermittent. Then It eventually decided to start again one day. Ran rough. For a while I could get it to start and I would troll to fishing spots with it, but it would shut off and not want to start again for a while. Then I took it out and gunned it, it proceeded to plane out and run great at high speed, got a couple miles down the lake and throttled down slowly and it cut off and wouldn't start again. Now I can get it to run barely but it likes to shut off unless the throttle is advanced and it sounds bad. I am almost certain it must be the stator/trigger. What do y'all think? (yes I tested compression after all of this and was still 130 on each) (I also retested spark and saw spark on all three)
Test for stator, trigger, switch box, shine the wires connectors before doing so, check the rectifier too...they tend to corrode/rust alot...
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,044
Correct.---Pull starter apart for inspection.----If starter does not spin flywheel fast enuff there will be no spark.-----The common answer on posts of this nature is --" there is nothing wrong with the starter "
 

Ed27518

Cadet
Joined
Oct 12, 2019
Messages
15
Correct.---Pull starter apart for inspection.----If starter does not spin flywheel fast enuff there will be no spark.-----The common answer on posts of this nature is --" there is nothing wrong with the starter "
It is a very strong starter, turns over real fast. and it does in fact have some kind of spark at the moment
 
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