40hp mercury ignition systems

[Zberry1985]

i guess i'm just looking for opinions on whether or not this idea will work. i'll lay the story out below and you guys can let me know if i'm crazy or if it just might work. any suggestion on which parts to use from which motor are appreciated.

I picked up a beautiful monark 1542 mod v boat with a 1973 mercury 402 motor, SN 3727106, both manual and electric start. the motor had a mouse nest in it and all the wires were chewed off or super brittle and falling apart. no problems replacing wires but the stator wires are incorporated into the housing and no way to replace them, so a new stator is needed. I can find them for $100 used or $200+ new. while looking at the new ones i noticed that they cover multiple years and motor models. also while looking for used a stator i found a 1982 40hp motor SN 6053095 with a bad block for cheap. seeing that the aftermarket stator would replace both the 1973 and the 1982 version i figure the 1982 version would also work on the 1973 version. so i picked up the 1982 motor with the bonus of other extra parts if needed.

turns out there are a few differences between the two, i'll try to lay them out best i can. on the 1973 model the stator coils are encased in plastic and make a complete rind, magnets are also around the entire inside of the fly wheel. on the 1982 model the stator is like a horseshoe and has 2 coils on one side and 3 coils on the other side. the flywheel also has just 2 magnets on the inside. also the trigger coils are different 1973 has a spring and pin to complete the loop, the 1982 is a solid ring.

well not being one to give up i decided to try it anyway except i was quickly stopped by the fact that the bearing end cap that holds the trigger and stator are not the same. so i can't just bolt the 1982 stator on the 1973 motor cause the bolt hole dont line up. but i noticed the bearing end cap bolt holes are the same so i put the 82 end cap onto the 73 motor. fit good and satisfied on a possible solution that is where i stopped for the day.

so going forward the plan is to use the 1982 bearing end cap, trigger, stator and flywheel on the 1973 motor. think it will work? should i also use the 1982 switch box and cylinder coils?

extra notes- the service manual sticked on the forum is great thank you!. but i want to note that it show the 1973 motor as a type II ignition with points. imagine my surprise when i pulled the fly wheel off and there's no points. so not sure if the service manual is wrong of if this motor was tinkered with before, possibly electric start was added and stator was changed then? not sure.

 

[Zberry1985]

i finally got the motor all back together and it fired right up. it actually sounds to be running pretty decent but i think there might be a timing/spark issue. playing around with a timing light its real close to to my mark on the fly wheel but then it also gives the occasional flash elsewhere and i thinks it's picking up the spark for the other cylinder. not sure if it's my harbor freight timing light or an actual second spark. i haven't had a chance to test higher rpms yet. now that i know it runs i have a tach ordered and some other parts.

one odd thing is when i adjust the idle mixture screw the rpms go up the closer i get to bottoming out, about 1/8 turn out is highest rpm. any guess as to why that is?

 

[JL8Jeff]

Off the top of my head, I think a lot of the Mercurys are best set around 1/4 turn out. If it's off too much, you can get that Mercury "sneeze" at idle. It's more like a stumble but it takes some fine adjustment on a warmed up motor while running it in gear. So you can do an initial set of it while on the trailer but plan on fine tuning on the water. I think when too much air mixes in, it will cause a lean out and the "sneeze" or stumble. I've had to adjust a 90 hp and my 60/45 jet and it takes a little while to keep adjusting each one (depending on how many carbs your engine has). I think as you turn the screw in and there is less air, the mixture is the right ratio which raises the idle until not enough air gets mixed in.