1983 Mercury 80 Questions

[axlr8]

Just acquired a 1983 Mercury 80 hp outboard motor, I am looking for known common issues with these motors, and things to check for before I put it onto a boat and try to hit the water.

Some things that I know are already problematic are the lower unit needs a skeg repair job, I'll need a new propeller as well. I found a badly corroded power wire that goes to the #4 cylinder coil, I assume that I can replace that with a new wire, somewhat hassle free.

Some of the things on my list of to do's with the motor are:
-New Impeller
-Skeg repair
-Propeller (to match boat it will be installed on)
-Check/repair visibly damaged wiring
-Gentle scrub/degrease of whole motor
-Paint touch up after installed on boat.

If there is anything else I should be servicing/looking at while I have it on the motor stand, I would like to hear anything about it, I have alot of experience with small engines, mainly 2 stroke, but not much at all when it comes to outboard motors.

 

[Chris1956]

That motor likely does not have a thermostat. It relies on a good impeller to keep it cool. So make sure the water pump is kept in good condition. In addition, fresh 50::1 fuel helps it run smooth and cool.

​Finally, make sure the prop allows the motor to reach the max recommended RPM at full throttle and with a standard load.

 

[axlr8]

Thanks for the quick reply Chris1956, I fully intend to install a new waterpump/waterpump rebuild kit, that is one of the key things that I was raised on,"if your boat isnt 'pissing' with in 30 seconds, shut it off" was what I was told every time i took out our little 14' Alumacraft and 15 Hp Johnson.

Fresh fuel should never be an issue either, I have seen first hand what stale fuel can do to an engine, and even worse, what stale fuel with 10+% ethanol can do to an engine.

Is there some kind of special propeller calculations or chart that I should be using to find my correct propeller size?

 

[racerone]

Step # 1 is a compression test before you spend a single $ on it.-------Or remove bypass covers to inspect pistons and rings.

 

[Mohawkmtrs]

Once everything is good and before you put it in the water, inspect/change gearcase lube and replace the crush washers.

 

[axlr8]

Ok here is an update on the motor. I did a compression test and could only get my tester to 3 of the 4 cylinders, 115-110-110-??? Now my tester may be a few PSI low but the cylinders are all within the usual 10%+/- range that we shoot for on multi-cylinder tests.

I cleaned my carbs the best I could without installing kits, and put some fresh mix in a tank and primed the motor, I got it running and put the lower unit in a barrel of water and let the motor idle for 15 minutes, once warm, it starts instantly, which is a nice thing to know. So I packed up for the night and put it in the shed until I can order the parts to get it up and correctly re sealed and lubricated.

In the mean time, I'm headed to look at a boat this evening and hopefully I can pull the trigger on it. I will keep you guys updated on the motor.

 

[axlr8]

Here are a few photos to look at, they are pretty self explanatory.

 

[axlr8]

Here is a short clip of the motor running.

 

[racerone]

The wiring is a problem on that vintage of motors.---It will need attention or it will leave you stranded.

 

[axlr8]

What can I do to fix it? Mercury sells a new harness that feeds the #3 & 4 coils, but it is 55 bucks. From the brief once over that I gave the motor, that was the only problematic spot. I have been told that those coil wires are well known for degrading..Is there a known and dependable fix for those wires?

 

[axlr8]

How can I tell what style waterpump my motor has? Im given the choice of a kit to rebuild to rebuild a once piece housing or a two piece housing. Or is there no way to tell without dropping lower unit?

Secondly, how do I determine if there is one or two fuel pumps in the motor? The feed line passes through one housing that I can see and feeds the 2 carbs with 1 line that tee's off at the carbs. Im assuming I have a single fuel pump motor???

 

[Chris1956]

You should see the two fuel pumps, if it had them. Trace the fuel line from the quick connect to the carbs. I think the older motors had the twin triangle fuel pumps. Newer motors had a single figure-8 shaped fuel pump, which is what I would expect you will find.

​I would expect that motor to have a waterpump base and cover. Look on the crowleymarine web site and see. You can look it up by year and HP. The serial number can be indexed on the maxrules web site to obtain the exact year.

 

[axlr8]

Thanks Chris1956, I will do a little looking and see what I can come up with. Im fairly certain that I have the single fuel pump.