Reviving a 1971 Mercury Model 500 50 HP

[keegan.bye]

My wife's grandfather left behind an old alumicraft with what I think is a '71 Mercury 500 50hp (serial # 3095395) outboard hanging off the back. It's been sitting since the early 90's on the edge of a lake in MT. I took the tarp off it on my last trip up there, took the covers off and it looks to be in reasonably good shape. I pulled a couple plugs and to my surprise, it sparks.

I cleaned the boat out and have started thinking about what I need to do before I try to get it running. The manual has a few grease/lubrication points, I figured I'd start with those, as well as a new impeller as there seems to be a consensus that those are an easy, common sense item to replace. Figured I'd run some compressed air through the output hole while I'm at it. The throttle and shift linkage seems to work smoothly. As viewed from the propellor end, there is a small black piece on the left side of the motor that has a wire that's falling apart. Can't seem to figure out what this is, my best guess is a mercury switch? I'll circle it and attach a picture.

Any input on what to do before trying to start it would be great. I've seen a few mentions of using non-ethanol gas when making its 50:1 mix, is that a thing? Also, how available are carb rebuild kits for this? I've looked for them and haven't really found anything.

Thanks in advance!

 

[makomark]

you can find the carb kits here:

Mercury Marine 500 Carburetor Assembly, Complete Parts

Mercury Marine 500 carburetor assembly, complete parts. Buy a genuine Mercury Quicksilver or aftermarket part.

www.marineengine.com

agreed, the circled items is the tilt switch that should kill the ignition if the engine hits something while at speed...

I'd also add the fuel pump service kit to the to-do list.,.. and change the gear lube when you do the impeller...

Also make sure the transom wood (filler?) is solid...I'd worry about the spark plugs after its running if they are sparking well.

the non-ethanol fuel is a good thing for most boats, especially of that vintage...ethanol will eat up the old rubber.

probably clean out the fuel tank and you may not have any problems...good luck

 

[keegan.bye]

you can find the carb kits here:

Mercury Marine 500 Carburetor Assembly, Complete Parts

Mercury Marine 500 carburetor assembly, complete parts. Buy a genuine Mercury Quicksilver or aftermarket part.

www.marineengine.com

agreed, the circled items is the tilt switch that should kill the ignition if the engine hits something while at speed...

I'd also add the fuel pump service kit to the to-do list.,.. and change the gear lube when you do the impeller...

Also make sure the transom wood (filler?) is solid...I'd worry about the spark plugs after its running if they are sparking well.

the non-ethanol fuel is a good thing for most boats, especially of that vintage...ethanol will eat up the old rubber.

probably clean out the fuel tank and you may not have any problems...good luck

Thanks for all the advice! Any idea how to change the gear lube, and what to replace it with? The manual has some odd terminology when it comes to lubricants, nothing with conventional viscosity figures (ei: 75W-90). There are two bolts down on the left side, they look like the classic fill plug and drain plug configuration, am I down the right track with that?

 

[makomark]

on the gear lube, get the quicksilver stuff...and the pump makes it easier...and take the prop off and clean off any mono and grease the splines.

As far as draining the old gear lube out - there should be another drain plug, on the lower half of the 'bulge' in the gear case where the prop shaft and gears are...and its not visible in your pic. On the two drain plugs that are visible, you only need to use the forward of the two - it should have VENT cast into the housing next to the plug...the other (going on memory) is the old style FLUSH plug.

you put the drain collection container under the gear housing and remove the two drain plugs described above...and let the housing empty out...you fill the housing from the BOTTOM hole, until it flows out from the upper hole...once the housing is filled with new lube, replace and tighten the upeer VENT plug...then remove the filler hose and replace the lower drain plug and tighten...if that plug has the magnetic tip, swipe it clean with a rag or two.

If you try to replace the gear lube from the top, you will be replacing the lower unit in short order...

you can usually ask Mercury to send (or email) you a copy of the owner's manual...you can get their contact info from there www page...they may ask for your serial number to ensure having the proper data.

 

[brickslap]

I have one that looks the same, which I have been working on. I replaced the starter and solenoid, and I could start it despite the key being broken off with a screwdriver, but I got zapped every time. I bought an Amazon ignition switch and matched up all the wires using a volt meter end to end to make sure the correct wires went to the correct places. I melted all the wires. Now, I am slowly replacing all the wires in the motor. I have been running normal ethanol-free gas, and it works. It came on an 18 ft Glaspar, and they said that it didn't work, but they were running mixed gas through it. It runs great on unmixed gas. The starter was a little bit intermittent before with clicks, and a new one makes it fire right up. I was running it with the case open so I could run to the back and pull the choke every time, but the new ignition made the auto choke work after greasing it up before the wires melted. I think I need a fuse like yours has with the push button reset on the solenoid.

 

[brickslap]

I have one that looks the same, which I have been working on. I replaced the starter and solenoid, and I could start it despite the key being broken off with a screwdriver, but I got zapped every time. I bought an Amazon ignition switch and matched up all the wires using a volt meter end to end to make sure the correct wires went to the correct places. I melted all the wires. Now, I am slowly replacing all the wires in the motor. I have been running normal ethanol-free gas, and it works. It came on an 18 ft Glaspar, and they said that it didn't work, but they were running mixed gas through it. It runs great on unmixed gas. The starter was a little bit intermittent before with clicks, and a new one makes it fire right up. I was running it with the case open so I could run to the back and pull the choke every time, but the new ignition made the auto choke work after greasing it up before the wires melted. I think I need a fuse like yours has with the push button reset on the solenoid.

One extra thing you have in your favor is that my shifting shaft is broken somewhere, and so I have only forward. I circle in and kill it early and hop out of the boat to drag the thing to shore.

 

[racerone]

I hope you are mixing gas and oil at 50:1 on this motor.-----If not . it will come to a dynamic halt and be worth 12 cents / lb.