1968 Mercury 39, 3.9hp Outboard - Restoration

[Jhollenbeck]

I am in the process of rebuilding a 1968 Mercury 39, at this point I have rebuilt the water pump, new fuel lines and pump disphrams, cleaned and rebuilt the carb and new lower gear oil. I am able to get the motor running with starter fluid, it does not idle for long but if I throw it in forward it stays run. I have a few general questions to understand more about this motor and how much better this old technology will run.

1. Should the water pump be pushing water through when I am in neutral? I do not have water flow unless I have it in gear, trying to determine if this is the design of the motor or if there is issue with the water pump.

2. Should I be able to start the motor without using starter fluid? If this were 1968 I would assume you wouldn't need to use starter fluid to fire it up but is there issues if I need starter fluid everytime I want to start it up now?

3. I was told by the previous owner that it never idled well, is there something I can do to correct that or is that a limitation of this motor?

 

[racerone]

It should pump water as soon as the motor starts.----In gear or neutral has nothing to do with pumping ability !!-----But a very , very common mistake is not enough water in the test bucket.-----Water MUST be 6 or 8" above the impeller.-----You should not need to use starter fluid to start it.-----Some will argue but that motor in good condition will idle troll all day long.-----So perhaps you have some trouble shooting to do.

 

[Jhollenbeck]

Thank you for the feed back, I'm 99% sure I have enough water in the test tank since I did have a good flow when in forward. My initial thoughts after reading your response is I may need new gaskets, there may not be enough pressure for the water to go up the tub without being in gear, does that make sense?

 

[racerone]

As clearly stated the shifting has nothing to do with water pumping.----Find the real problem.-----Motor should pump just fine in neutral right after starting !!!

 

[Jhollenbeck]

Understood, unfortunately I do not have a good understanding with this motor so I am not sure where to go to next in finding the real problem that's why I'm posting hoping for some suggestions. I have done all I can and cannot really find much online for this issue.

 

[Quicksilver]

If you want to really fix it you'll need the manual https://www.oldmercs.com/category_s/1188.htm there are things like the points and timing that need attention in a motor of that vintage; you should be using the choke to start as well as advancing the throttle to the start position in Neutral.

 

[fitz73222]

Get the 1966-1974 Factory manual, scroll down on that link provided, its there for $79. Then you will understand what needs to be done to get it to start and run well. I have three of those engines in my collection and they will start on one pull cold and purr like a kitten when warmed up. Don't ever use starting fluid to start an outboard since it acts like a solvent and washes the oil off of the bearings and strips the lubrication inside the crankcase.

 

[Jhollenbeck]

I do have a digital copy of the parts and the user manual. Also I did replace the points, the ones in it were bad and would not get a spark without new points. Set the points spacing to .02 and was able to start it up.

 

[Quicksilver]

Are you priming it with the bulb on the fuel line? Use the choke closed until it "kicks" then open and pull. When it's running in Forward in the slow range try turning the low speed needle in and out slowly to get the idle right. What oil/gas ratio are you using?

 

[Jhollenbeck]

Using a 50:1 ratio per the manual. I will give the rest of your suggestions a try tomorrow and see if I get better results.