1978 Mercury 90hp outboard

[TyeCope122]

I need help with the wiring and trying to test for spark on my 1978 Mercury 90hp. If any one has any wiring diagrams that would be great appreciated, im just trying to check for spark and get this thing running.

 

[racerone]

If those are the compression values it is time for a rebuild or another motor !!

 

[TyeCope122]

If those are the compression values it is time for a rebuild or another motor !!

You can’t give up on something that easy or you’re never gonna get anywhere with any motor. Nothing a little lube can’t fix. The rings are probably just stuck but there’s still a good chance it will run with some work.

 

[racerone]

It might run but not very well !!----Easy to inspect for damage.-----Good luck with it.

 

[TyeCope122]

It might run but not very well !!----Easy to inspect for damage.-----Good luck with it.

Thanks for your input. I can tell you’re not very knowledgeable when it comes to these sorts of things but thanks for your input anyway.

 

[racerone]

I could rebuild that motor with hardly a glance at a manual.-----I think you need to learn a wee bit of trouble shooting !----Good luck with it.----Note ---I own about 10 or 12 inline 6 Mercury motors.

 

[TyeCope122]

I could rebuild that motor with hardly a glance at a manual.-----I think you need to learn a wee bit of trouble shooting !----Good luck with it.----Note ---I own about 10 or 12 inline 6 Mercury motors.

Who says anyone needs a manual? I’ve rebuilt chainsaws all the way up to jetskis without any manual. Being able to rebuild something without looking at the manual is not the greatest accomplishment of the century. How come you’ve got so many inline 6’s? Do you not wanna fix the easy problems at hand so you just buy new parts to replace the ones that can be fixed easily? Clearly you’ve never experienced or taken an outboard that’s been sitting for awhile and got it running without throwing a bunch of new parts at it if you don’t have to. Seems like you don’t have an important trait when it comes to working on outboards which is determination.

 

[jimmbo]

Thanks for your input. I can tell you’re not very knowledgeable when it comes to these sorts of things but thanks for your input anyway.

You certainly got that wrong. Racer was being Honest, and trying to keep you from wasting a whole pile of Time and Money. Compression numbers are horrible, and there is a very slight chance that the rings are stuck, but there is a greater chance that they are not. Every High Tension wire is cracked, well actually just about every wire on that motor needs to be replaced. Then there is the Matter of the Gearcase. Even the Cowl Mount Isolators are cracked and twisted.
I know that is not what you want to hear, but it will cost far more to restore this motor than it would ever be worth.

 

[Faztbullet]

Rings do not stick in a outboard unless submerged, especially a single cylinder on a multi cylinder motor. Pull the transfer cover and inspect piston. Also mount the starter correctly/

 

[Chris1956]

You are missing the coil. It bolts to the three thin screws in the block directly below the distributor cap.

The rotor is non-removeable and $200+ to replace if you do the work. The cap is also $200+, but they last a long time.

The spark plug wire conductors are stranded stainless steel. They should have zero resistance.
Replace the green wire from the switchbox to the coil as the insulation is bad.

The starter needs a ground cable, where that long bolt is on top of the starter motor. It connects to one of the front cowling bolts, opposite the distributor ground.

A wiring diagram is avail at the maxrules web site. Make sure you choose the distributor CDI ignition version, as different year L6 motors used different ones.

Your compression numbers aren't great. The #3 cylinder is likely damaged, so inspect that piston via the center transfer cover on the starboard side.

 

[merc850]

Here's a wiring diagram - I would just replace the wires, the waterpump impeller, the gear lube and not touch the timing. After all that see if it will run. The coil should be available on this site. The switchbox terminal nuts seem to be rusty if so remove and clean the terminals.
An AD tach is available and is a good idea it connects to one of the yellow/red wires from the rectifier.

 

[jimmbo]

Rings do not stick in a outboard unless submerged, especially a single cylinder on a multi cylinder motor. Pull the transfer cover and inspect piston. Also mount the starter correctly/

Carbon buildup will cause sticking, that doesn't happen from submersion

 

[racerone]

Seen lots of rings stuck with carbon.

 

[fatlenny]

Seen lots of rings stuck with carbon.

Don't waste your time, don't let him get to you. He came on here looking for information because HE is "not very knowledgeable when it comes to these sorts of things". Some people just want to argue.

I hate to see people come on here asking for advice then just being rude when they get some. When my ignorance of some wiring came up last summer, I spent 3 minutes on Google and found wiring diagrams for my 51 year old motor. I wouldn't wait hours or days for an answer on a forum then be snippy to people about the replies I got.