1989 mercury 90 hp

[WWTSE670]

Hello. I have a 1989 mercury 90 that I have been struggling with for a few season now. This year I went to start it and it didn't fire.
This motor has always been difficult to start, seems like it floods easily and once it does changing the plugs is the only thing I can do to get it going. Once running the motor seems to idle only on two cylinders, once I power it up it hits a flat spot till the thee cylinder kicks in then runs out great. Running it on step it runs good and doesn't seem to have performance issues at speed.

I run quite a bit in cold water and have noticed that the water coming out of the motor is always ice cold. Don't if it should be warm.

I have begun troubleshooting the ignition system and it seems like the stator doesn't check out but I would like some opinion before replacing parts.

 

[JDusza]

Re: 1989 mercury 90 hp

Welcome to the forum. There's good advice here. Let's see, ...
Without serial number, I will assume we must be talking about the 90 hp 3-cylinder. Serial number will help.
Yes, do not throw money at ignition problems. Parts are way too expensive.
Sounds like compression is okay, but wouldn't hurt to test it to note where you are. The rest is ignition and fuel.
You might be able to find out which cylinders are working and which ones are not by pulling the spark plug wires one at a time while running. When you remove the spark plug wire from a a cylinder that's not working, there will be no change in the engine sound. When you pull a plug that's working you will hear the engine performance falter.
Spark
Remove all the spark plugs so there's no risk of starting.
Scrub clean, with wire brush, not steel wool or sandpaper, all electrical connections on the coils and switch box.
Get yourself (from auto parts store or make) an air gap spark tester. You will need this to verify electrical power, spark, to all cylinders. When cranking, you should have enough spark to jump 3/8" air gap.
Once you see what's firing, you can swap coil inputs and outputs to determine which inputs, outputs and grounds are working.
To troubleshoot the stator and trigger mechanisms you will need a DVM with peak hold, a DVA, about $25, and the CDI ignition troubleshooting manual. Go to their website CDI Electronics | Outboard Motor Parts | Ignitions | Marine Engine Diagnostic System | Stators | Ignition Packs | Regulators | Coils | Wiring Harnesses and get to troubleshooting guide and look up your model.

Fuel
Carbs could use a good cleaning, low speed and high speed jets, etc,... maybe rebuilds if they're humble. If you continue to have problems after the ignition is correct, then go to the carburetor that corresponds to the bad cylinder.

J

Cooling, yes, you may expect warmer water than the intake but if you're not running top speed in cold, the output water may not appear to be warm. Can you touch the power head or is it too hot? You can usually touch 110-120 degrees, 150 -160 is gonna hurt. Let's get the ignition and fuel reliable first.

 

[WWTSE670]

Re: 1989 mercury 90 hp

Appreciate the response, tonight is the first night I've been able to work on the outboard in the past week.

Apologies the serial # is 0B181131 don't know exactly what year the motor is.

So far with the inline spark tester I have no spark on any of the three cylinders... This isn't with an air gap tester like you mentioned just an inline tester.

I am wondering if this is how a stator usually fails? Or if there is something else to check that would explain this? I am going to clean and use a little dielectric grease on all the connections tonight and see if that helps.

Fuel system was cleaned and floats adjusted last year.

Appreciate anything and all help!

 

[WWTSE670]

Re: 1989 mercury 90 hp

Update

After cleaning all terminals and monkeying around I have spark on one cylinder. I changed around coil inputs to rule out bad coils but they all checked out.

Seems like in order to continue on I need a dva, can this be bought locally? Cdi wants 100 bucks for there's wondering if there is a cheaper alternative.

All help appreciated

 

[WWTSE670]

Re: 1989 mercury 90 hp

Another night spent on the motor and I found a completely rotted white/blk wire from the trigger to the switch box. Does this suggest a failed part elsewhere causing excessive heat?

Appears like the trigger has to be replaced? Is there a good way of locking the flywheel on these things other than buying the merc part?

Haven't had any responses lately but will continue to post until I fix this thing,

 

[TD_Maker]

Re: 1989 mercury 90 hp

I just parted out a motor just like yours, so I have some experience with it....... Mercury had an issue with wiring in this generation of motors. I have found that the wiring from the stator, trigger, and switch box will often rot from the inside out. I have actually found bare wiring running from the trigger to the switch box. The insulation will just fall off the wiring. Pull your flywheel, and check the stator and trigger wiring carefully. The trigger wiring (at the bend) will often be the culprit....and it is difficult to repair. If you can cut the wiring back far enough, a new wire may be soldered onto the shorter piece and heat shrinked....if you are lucky.
Also, check the terminals on your switch box. These wires will often rot and become disconnected at the screw bolt fasteners on the switch box. Once you think the wiing is solid, then check to see if you have spark and gp from there.
For what its worth, used Stators, triggers, and switch boxes can often be found on Ebay.

 

[TD_Maker]

Re: 1989 mercury 90 hp

ps. Your life would be much easier with the Mercury flywheel puller sold on Ebay. Simple to use although I did manage to get mine off with a 10in gear puller.