Mercury 850 85hp. Good engine or stay away?

[Bman2895]

Looking at an older caravelle bow rider in beautiful shape. Boat is a 1974 model. I assume but haven't confirmed if the mercury is. If it's the older distributor setup should I stay away from it? Guy says it's been garage kept and hasn't ran in awhile.

 

[Bman2895]

Well I went ahead and bought the boat. It's basically brand new I'm the second owner and he said the boats maybe been to the lake 10 times it's whole life otherwise it's been garaged.

I'll check for spark before I bought it had good strong spark on all four. Brought it home hooked some fuel to it and it busted right off. I only ran it for a few seconds due to a stuck float but that did unstick.

It does have the degrading wire issue. The stator wires and all the wires coming in inside the cowl the wire coatings are all falling apart. Now everything is currently working and I feel like if I touch that mess it will stop working. I don't know if I should just replace that whole harness or if I could get away with a bunch of liquid electrical tape. Even though the engine is original to the boat I'm pretty sure it's incredibly low hour I doubt I'm going to keep it simply due to the cost of parts and I'm kind of spoiled to power tilt and trim.

Any tips for this old engine would be helpful

 

[Chris1956]

Unfortunately, the engine wiring on those older Mercs fails in time. Take a look at it, to see if the insulation is falling or has fallen off the wires.

The distributor ign worked fine, but replacement parts are real expensive. The rotor was non-replaceable and $200 or more. The dist cap was $150 or more, and the trigger was $250 or so, if you could find them.

 

[DeepCMark58A]

There is not a lot of wire in those motors, you can easily rewire a motor. I have a 1957 Mercury I can easily get parts for. Do a compression test.

Post some pictures up please.

 

[Bman2895]

It's definitely failing. And fallen off wires. And yeah I noticed it looked pretty straight forward to make the wiring for it if I wanted.

Id love to keep it with the boat being original, if I can get it reliable.

 

[jimmbo]

The 4 cylinder Merc 850 was first marketed in 1973, the last year for it was 1977.
Mercs of the 50s, 60s, 70s, and into the 80s used Wire that did not hold up well over time. Mercury must have bought enough of the stuff to go to the Moon and back at least a couple of times.

A Good Spark would be one that can Jump a 3/8" gap.
First thing you need to do is replace the Pump Impeller.

 

[Chris1956]

You can likely buy a new wiring harness for the motor. Get a part number off crowleymarine and search on it. Sierra used to make one if memory serves. CDI Electronics may have some stuff as well.

Check the spark plug wires. They were called "Yellow Tiger Tails" and use to be available from Surplus Unlimited.

You can put adhesive lined shrink tube on the distributor wires and stator wires, if the conductors are in good shape.

 

[1960 Starflite]

I have a 1975, 850. As stated the wiring was terrible. I rewired the engine, the hardest part being the stator. I had to cut the junk wire actually into the windings. To solder, you Must use lead core and paste flux. Then slip shrink tubing over it.
The distributor wire is a different source and was fine.

The junk wire doesn't stop there. The control cable to helm is also made of junk wire.
CDI is a source of both engine and control replacement cables.

Once the wiring was replaced, the engine is a Great improvement over the 1965, 650 magnito driven Mercury on my 24 ft Pontoon.

 

[DeepCMark58A]

When I rewired I have access to THNN wire oil and gas resistant wire.

 

[Chris1956]

I always liked the 850. I thought it had good power in a compact size. Since it only had 2 carbs (vs the IL6) it was easier to tune, and I thought it ran very good for a 4 cyl 2 smoker.

 

[Bman2895]

I have a 1975, 850. As stated the wiring was terrible. I rewired the engine, the hardest part being the stator. I had to cut the junk wire actually into the windings. To solder, you Must use lead core and paste flux. Then slip shrink tubing over it.
The distributor wire is a different source and was fine.

The junk wire doesn't stop there. The control cable to helm is also made of junk wire.
CDI is a source of both engine and control replacement cables.

Once the wiring was replaced, the engine is a Great improvement over the 1965, 650 magnito driven Mercury on my 24 ft Pontoon.

I haven't inspected the wires up to the helm yet. It sounds like I should re-wire it vs just seal it and let it ride.

And yeah everything wire wise on the distributor side looked fine.

And this is on a 1974 Caravelle Tarpon model. Alittle over a 15ft boat.

 

[Bman2895]

I suppose the wires to helm are fine? Not sure how to really inspect them seeing as they're kinda sealed in that jacket?

After looking at the engine side harness I probed alittle further down the harness towards the cowl and im not sure theres any really "good" wire left to splice to. Its looking like I may purchase a replacement harness for that.

The stator wires are similar the coating is still pretty cracked and ugly further up the wire. I may just try shrink tubing to protect those.

Got a water pump kit on the way.

 

[Chris1956]

The quick connects often fail. I had to fix the quick connect ign power wire on my '77 in the mid 90's. I eventually needed to replace it entirely.

 

[Texasmark]

I bought an 850 new in the '70's time line. Right at the top of my engine purchases for excellent performance. I bought it with a new Bass Boat purchase after my family quit the water actives as they grew older. Back then I had an 18' Caravelle bow rider tri-hull I bought new in 1972 with a 125 Johnson....another great purchase.

 

[Bman2895]

Fired it up on some water horns today. Seems to run decent.