1979 Mercury 175 turns over but intermittently start

[JC1979]

Inherited a 1979 Mercury Outboard. It ran great for my dad, but I can’t get it started. Already replaced battery, spark plugs, and starter solenoid. I found a loose fuel line, attached it, and it started (and roared!), but then I did some more work (installed switch on starter solenoid because it is harvesting power from an accessory), and now it won’t start (with switch closed, obviously). The starter runs and the flywheel turns, but the engine does not turn over. The fuel is fresh. I think it is getting fuel: The primer bulb gets hard and it pumped through the fuel pump when I disassembled it. It just seems like the plugs are not sparking. The boat sat for 3 years before I inherited it. Any insights would be greatly appreciated. It’s a family heirloom!

 

[JC1979]

Clarification: It cranks but doesn’t fire. (But it did two days ago.)

 

[Tassie 1]

Use a compression tester to test compression
also check for spark

Read the stickies above for info re bringing motors back into service

 

[Faztbullet]

Battery, starter and cables have to 100% as if not the voltage drop will not allow choke butterflies to pull tight and choke engine...

 

[Chris1956]

Check the engine wiring harness. On a lot of those motors, they start to degrade. If the spark killer wire (orange wire), is grounded, you will not have spark.

Missing insulation on other wires can have other bad effects.

 

[JC1979]

Checked: No spark on 1, 3, 5. (But 2, 4, 6 spark.) Orange wire looks okay. Wire to idle stabilizer is questionable but others look okay.

 

[JC1979]

What do you mean by “read the stickies above”? FAQ sections?

 

[Tassie 1]

At the top of each page is a yellow section with really helpful posts that folk have put up,

there is at least one re your situation, could be in the engine repair etc forum

 

[Chris1956]

OK, so one swittchbox isn't firing. Swap stator leads to switchboxes and see if no spark condition follows wire switch. If so, stator is bad.

CDIElectronics has a troubleshooting guide for your ADI ignition on it's web site.

 

[JC1979]

Swapping the stator wires moved the spark to the other side. So it’s the stator, or maybe the switch box? Stator wires look ok.

 

[Chris1956]

If the problem moved when the stator wires were swapped, it is likely the stator.

Remember your motor has 1 stator, 2 switchboxes and three triggers. So the stator is shared across all six cylinders, the switchboxes control 3 cylinders each and the triggers share 2 cylinder each.

I would recommend a full link and synch after the stator is replaced.

 

[JC1979]

Is there something else I should check first? (Before I pull that stator.) Ten days ago it started and ran fine.

I am working through the Ignition Troubleshooting portion of the manual with the amp meter but would appreciate any hints on likely culprits other than the stator. I did take before/after photos so I think my wiring is correct, but the coils, wires, switchboxes are original 1979 so plausibly need replacement.

The local Mercury dealer actually has a stator that fits, but I need to collect the tools to pull the flywheel, etc. (And I am on the waiting list to get help from the local shop. Is it really that hard to correctly remove and reinstall these parts? The manual is full of warnings.

Thank you for all the help - I really appreciate access to this level of expertise.

 

[Chris1956]

There is a tool to remove the flywheel. It is not expensive and useful for other jobs as well, as it is a combo lifting ring for the entire motor, and flywheel puller.

I would also recommend an OEM service manual.

 

[Faztbullet]

Be careful on the stator as the older ones used a thinner stator and a newer style will rub flex plate of flywheel...You can cheat. Remove sparkplugs, turn flywheel to TDC mark, remove hub bolts on flywheel, lift off and replace stator, reassemble realigning TDC mark.

 

[JC1979]

Whew! Flywheel nut is off (impact wrench) and flywheel/stator are out (used flywheel tool as suggested). Stator is definitely fried. (Ohm-meter.) I read somewhere (internet?) that some other parts tend to get smoked with the stator? Switchboxes arrive tomorrow. (May be fine.) Trigger tests out okay. (Using reference Ohms from an OEM manual.) Rectifier shows no continuity anywhere so I will order one. (I think I sparked (shorted) it with a careless wrench.) Anything else?

 

[JC1979]

The CDI replacement starter has 7 wires but my old stator had six wires. Ground the extra black wire? (The old stator: red, blue, red/white, blue/white, yellow, yellow. New stator also has a black wire.)

 

[JC1979]

Replacement Stator has an extra black wire. (7 vs 6 on original.) Ground the black wire? Old: Red, Blue, Red/White, Blue/White, Yellow, Yellow. New one matches but also has red.

 

[Faztbullet]

Just ground it...

 

[JC1979]

And using removeable (orange) loctite just in case . . . . Ohms tested 30% below OEM manual but hopefully that works out fine.

 

[JC1979]

Okay, so the starter cranks but it still doesn't start. I have replaced the stator, starter solenoid, some corroded wires, voltage recitfier, spark plugs, and battery. Fuel is fresh so presumably good. Spark tester shows a good spark. The trigger tested as good with the multimeter. I disassembled and reassembled the fuel pump. Fuel drips from carburetor when I back out the brass plugs so fuel is at least getting to the carb. I can't find any airflow restrictions but I don't really know how to verify. I have new switchboxes that I will install tomorrow. Wire to the idle stabilizer is questionable but I think is okay. I did get it to start and roar for a couple seconds today, but then it dies. It started and ran for 10 minutes on the lake a few weeks ago before I started "fixing" it. Any suggestions on where to go next? Fuel pump?