Mercury Mark 20

Hey guys! Just picked up a Mercury Mark 20. It looks like it is the 16 HP version based on the serial number. It was super gummed up yesterday. I pulled the cowling off and cleaned it up with some cleaner which freed up a bunch of gunk! It was really dusty and gunky lol. The throttle arm turns freely now and I can engage all the gears. It was sitting for about 15 years is what the gentleman said that I got it from. It seems to have really good compression...I will check it today. I sprayed a little oil in the cylinders with some starting fluid to try to get her to roll over and try to lube up the internals. It pulls fairly smooth now. It seems to not be getting a spark... Any ideas? I was going to check the spark wires tonight and check the contacts... The spark plugs look ok...

Does anyone have any diagrams for this one?

I have a few questions about this motor if anyone can help me out.

How does the lower unit change the gear oil?

How do you get to the impeller for the water pump?

Thanks in advance for the help!

Spanky, stroll on over to the Antique Outboard Motor Club at https://www.aomci.org
and on the left side is a block "Ask-a-Member".
there are motorheads there that eat motors like yours for breakfast.
with the personal knowledge of these old guys, you will get the accurate
information you need in order to keep your motor running correctly for many years to come.

also, do the google search = many fine examples of restored motors will pop up
and, the good ole YouTube = several videos there of how to start it and keep it going.
https://www.youtube.com/watch?v=Sl4t0iFs4zA
https://www.youtube.com/watch?v=lO-RdVisfVU

good luck !!!

That's a very desirable motor. You're probably looking at a complete rebuild of the electrical. Original coils have probably disintegrated. There are many links and help available online. Take it one step at a time and restore her...

Shaugh said:

That's a very desirable motor. You're probably looking at a complete rebuild of the electrical. Original coils have probably disintegrated. There are many links and help available online. Take it one step at a time and restore her...

Click to expand...

I got ya. I am hoping that there is a decent chunk of the coils left...the guy rebuilt them or got new ones the last time he used it but that was like 15 years ago.

I am wanting to convert it to the new fuel pump so hopefully I can get the good attachment to go where the old 2 line system went. I want it to look clean!

So its looking like I need to get new spark plug wires. I tested them with my multi meter and they have continuity. Might have to check the other electrical pieces tomorrow if these dont work. I thought it was the connection to the coil, but when I checked it looks like its the connection to the spark plug. I will post pictures shortly!

So I pulled apart the motor. Was able to take the mercury flywheel nut off with some wood blocks and a pipe wrench. Had to strap the flywheel down with a ratchet strap but it came right off. The flywheel was able to pop off with some prying on the flywheel and tapping on the crank.

Then I pulled the coils and tested them for continuity. Looks like I am getting 4 ohms through the wire. The issue seems to be the sparkplug connector. I am going to redo the connection and get some new condensers and clean the points. The coils seem to be good.

I pulled off the carb and it's super dirty. It has the cork float and it looks nasty but it still floats. Is there something I can recoat the float with? I am going to get a carb kit and clean it up.

And lastly I pulled the fuel tank pressure pump off and cleaned up the motor there. The seal was super nasty but it cleaned up nice. I ordered a fuel pump from a mark 65 to put there to get a single line system. The good thing about the 65 pump is that there are 2 in the lot I ordered so I have a spare!

Spanky - here are some links to discussions about coating cork floats.
I think the general concensus is: if it ain't broke - don't fix it.
Aero Gloss model airplane fuelproof dope is probably the most popular.
found in any hobby shop and wal-mart. Midwest Products 654. a 3-1/2oz bottle.
- or - Testors Hot Fuel Proof Dope in smaller 1oz bottles.
https://aomci.org/forum/search.php?keywords=coating+a+cork+float&fid%5B0%5D=2&sid=ff6a647e9e1e7db31e8e552791d740f7

be very careful when working on the parts.
if you break something, you may not be able to find a replacement part. (cheaply).

Yup, electrical looks serviceable. Old Mercury coils are know for exploding into pieces...

It looks like you've got a very serviceable motor... Not a paperweight.... which is always a chance when you buy an old motor... buy a service manual... it will be worth every penny... If you get it totally restored and painted you'll need a stick to keep people away from it......