Newly acquired 1975 Mercury 850 85 HP outboard

[clemsparks]

Hi all,

I just got a package deal on a boat, engine, and trailer this past weekend. The boat is trash, but the trailer is nice and I hope to find that the engine is usable.

I'll be posting photos and more information as I gather it. What I know so far is that the title says it's a '75 model 85 horsepower Mercury.

The previous owner tells me he heard it run once and that the wiring needed replaced. I'm SURE there's more to the story than that...but that's all he's telling me.

So...for starters, I plan to check out all the components that I can. If things look good, I'll get a manual and prepare to get this engine ready for use. But I don't want to buy a manual if the engine isn't worth fixing...know what I mean?

So...I'll check the starter out first. It is off the engine right now (should make it easy to bench test). If it's good, I'll put it on the engine and check the compression (after oiling down the cylinders for a few days).

I guess I could use a little guidance on what to test after that. Coils for sure. Can the Stator be tested? What type of ignition do these have and how do I test that?

Any help is appreciated.

And like I said...I'll be posting photos soon and I'll get any other info that is necessary before advice can be given (just let me know what info you need).

Thanks for looking and helping an outboard newcomer.

Clem

 

[clemsparks]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Oh...I also just found what may be a good "parts engine" to have for this one. It was advertised as a '72 85 horsepower Mercury engine for parts ("missing some electrical parts"). However, on the phone the owner tells me it's actually an 800 model.

I wondered if anyone can tell me if parts would or would not interchange. Looking at the online iboats catalog, it looks like a '72 800 and a '75 850 do share some parts. I'm just not sure how much.

The prop on my '75 850 is pretty beat up...would the prop from the '72 800 work?

 

[clemsparks]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Ok All...so here are some photos.

The engine as it sits:

The serial number (hard to see but it is 4295178). Best I can tell, this does seem to correlate with a '75 model:

And what it looks like under the cover:

Thanks,
Clem

 

[Chris1956]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

I would think the parts from the '72 motor would work. I know the parts from a 1973 model will work. You might look up the parts list from both on the crowleymarine.com website. The '72 will have the old-style coil and rectifier, but the distributor and carbs will work, as will the gearcase and prop, cowling and lots of other parts.

 

[clemsparks]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Thanks for the reply!

I'm now curious...what style of ignition does the '75 have? And which is better...old or new?

Thanks again!
Clem

 

[Chris1956]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

The ignitions should be the same. The coils are a different form and fit, as are the rectifiers. The battery-powered distributor-based CDI ignitions were on all inline six motors from at least 1973 until the first part of 1979. These same ignitions were on inline 4 motors from at least 1973 until 1976 or '77. After that the inline 4 motors got the Alternator Driven Ignition (ADI), which is still used today on a lot of motors of several brands. Newest Mercs have CDM ignition, where the switchbox and coil are integrated and placed next to the sparkplug.

 

[clemsparks]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Thanks again Chris1956.

Do you (or anyone else) have any advice for me about what stuff I should test to evaluate how worthy this engine is of fixing up?

Things I know to test AND know how to test:

• Starter
• Compression

Things I want to test but could use some help figuring out how:

• Coils (just test for resistance? What value?)
• Stator (I know very little about them...is it just a continuity test?)
• Switchbox (I don't even know what these are or how many I have, let alone how to evaluate)

What other items should I add to the list?

I have a Digital Multimeter. If I can figure out what stuff I can test...I can give it a whirl. if all the major and/or expensive-to-replace components are in good working condition...I'll feel good about cleaning this engine up and putting it to use.

Thanks again!
Clem

 

[merc850]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

I have the same engine and if all the wiring is good and no spark it is probably the trigger.
If you are going to do a comp test you might as well check for spark at the same time.To check for spark ground all plugs and spin engine over.
Here's the wiring diagram for starters:

This engine is battery driven. Check the red wire on the switchbox ( large square box with nuts in front of carbs) for power when engine is attached to battery (12v) then turn on the key and check white wire on box for 12v. If no power on white - wiring harness or switch is faulty.

The stator charges the battery and reads .3 ohms; if running the engine should put out 15v.
Coil + to - .01-.02 primary, secondary 570-730 ohms.
A quick test to see if you're getting fuel in the carbs is to tilt engine all the way up and pump primer bulb gas should come out of the carbs. There is a filter near the fuel pump and if you have these carbs
filter screens inside. Someone is parting out one on ebay now.
No points in these motors there is an electrical trigger inside the distributor cap and DO NOT try to remove rotor it is molded on to the shaft.

 

[clemsparks]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

I just wanted to follow up and mention that I ended up selling this engine. The reason is that the title for it was stolen out of my car and it wasn't in my name or the previous owner's name (an "open title") so I just cut my losses and sold it to someone for a parts donor.

Clem

 

[new time boater]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

I recently purchased a 1975 850 outboard Merc. on a Bow runner, (fibre Glass 16 foot)
Took it out on the lake , it started fine, idled fine, but on the water when I opened it up (max throttle), it seemed very slow (MPH) . what can I do to making this boat & motor faster? Ive changed the plugs. fuel is new. mixed 50:1. it smokes a little. but that is ok ..Im told better to smoke a little then burn out or over heat the motor.I am new to boating , so please not too technical on the responses .. Thanks
Don

 

[kazek]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Visit/search for Clams Canino link and sync.it saved me on gas a lot.compression is the first to do,while on the water check tell tale for steady stream.some put pressure gauge ,if u want to be fancy

 

[new time boater]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Visit/search for Clams Canino link and sync.it saved me on gas a lot.compression is the first to do,while on the water check tell tale for steady stream.some put pressure gauge ,if u want to be fancy

Hello Kaz. I did get a tech perform a basic tune up & check . compression test, Is 130 psi all cylinders , very good spark. timing is spot on. all 4 plugs firing as they should. Carbs are very clean. fuel mix is good. it starts fine. However. out on the lake get to full throttle, I can only get 2100 RMP max. I understand my max RPM should be closer to 5000. & the 16 foot tri hull bow runner, should be just skipping across the water. Have you any suggestions that will not cost an arm and a leg? Hope this doesnt turn out to be a money pit....Grrrr
Don

 

[kazek]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Hi mate.First make sure butterflierflies on your carbs are fully open at Wide Open Throttle.you can do this with the engine off.check fuel lines for cracks,dings.if u are using plastic fuel tank,vent has to be open when engine is running.take the boat on the water again.find the way to pump the priming bulb on fuel line when motor starts to bog down ( or some one else).if engine picks RPMs, carbs are not getting fuel.fuel pump perhaps.

 

[kazek]

Re: Newly acquired 1975 Mercury 850 85 HP outboard

Those engines are a good runners.although wireing going bad is common on older types.keep an eye on it.you can easly splice the new wireing.tests showed that main component are in working order.fuel pump rebuild kit is ~5 bucks.3 bolts holding it(easy access),fuel lines can develop cracks ,collapse or clogs.with the motor on idle fuel would still flow but at WOT demand for fuel increases."carbs are clean" you could have sticking needle in one or both of the carbs,or in they need adjustment.carb kits are 20 bucks per carb.