Mercury 500 50hp - year unknown, have questions

[jhande]

If you haven't seen any of my other post, I'm new to boating. Late fall I purchased the boat setup in my signature. One scary thing is I can't find a plate to tell me the year of the motor.

The previous owner said he ran it the summer of 2019. He never stabilized the fuel and left it over the winter. When he tried to get it running the next summer he couldn't and blamed the old fuel and gave up. I know I have to start with cleaning and/or rebuilding the carbs which I'm fine with (I'm and old retired auto tech). I know enough that I should also change the lower unit oil before firing it up with the muffs to make sure she pee's.

But my major concern is that he "probably" didn't winterize it for last winter and I didn't know enough to winterize this year. I'm now concerned that I might have a junk motor on my hands?

What should I check and do to see if I can breath life back into her before I rebuild the carbs?
How can I order carb kits without knowing the year? Can't I'm sure.
When ordering the carb kit, is that usually for 1 carb or all carbs?

I use STA-BIL Storage Additive in my motorcycle and snowblower so I don't get nasty tarnish or gel in their fuel systems/carbs. That's the extent of my winterize knowledge that I ever needed. I will be looking into how to winterize an outboard.

Would or could I still use STA-BIL to winterize the fuel system or is there something better?
Any particular brand or type of 2-cycle oil I should use?
Only 2-cycle oil I've used before was for my old chainsaw.

 

[dwco5051]

If you haven't seen any of my other post, I'm new to boating. Late fall I purchased the boat setup in my signature. One scary thing is I can't find a plate to tell me the year of the motor.

The previous owner said he ran it the summer of 2019. He never stabilized the fuel and left it over the winter. When he tried to get it running the next summer he couldn't and blamed the old fuel and gave up. I know I have to start with cleaning and/or rebuilding the carbs which I'm fine with (I'm and old retired auto tech). I know enough that I should also change the lower unit oil before firing it up with the muffs to make sure she pee's.

But my major concern is that he "probably" didn't winterize it for last winter and I didn't know enough to winterize this year. I'm now concerned that I might have a junk motor on my hands?

What should I check and do to see if I can breath life back into her before I rebuild the carbs?
How can I order carb kits without knowing the year? Can't I'm sure.
When ordering the carb kit, is that usually for 1 carb or all carbs?

I use STA-BIL Storage Additive in my motorcycle and snowblower so I don't get nasty tarnish or gel in their fuel systems/carbs. That's the extent of my winterize knowledge that I ever needed. I will be looking into how to winterize an outboard.

Would or could I still use STA-BIL to winterize the fuel system or is there something better?
Any particular brand or type of 2-cycle oil I should use?
Only 2-cycle oil I've used before was for my old chainsaw.

The ID tag is located on either side of the swivel bracket (or transom bracket), and the instruction plate is located between the thumb screws above the steering tube. If the tag or plate has been lost or damaged to the point it can no longer be read, there’s a metal plug set in the powerhead that has the letter M and the serial number stamped into it. The precise location of the plug varies from motor to motor. Start with the basics. Do a compression test and a spark test first. Then worry about the carbs. Yes you will have to order a kit for each carb when you have found the exact year.
Oil should be type TWC-3. Chainsaw oil is for air cooled 2 cycle engines that run at higher temperatures and is not for outboards. 50/1 mixture for that motor. Those older Mercs were great motors but all the wiring should be inspected for brittle insulation and loose or corroded connections.
If the motor cover is original one of the Mercury gurus on this site can help you identify the year if you could post a picture.
Lower unit oil should be changed in the Fall in case there has been some water intrusion to protect the gear case from freeze damage over the Winter.

 

[jhande]

Thank you so much for the reply and info.

I have checked for the ID tag and it's not there, just like my missing VIN# on my trailer (Found out the old COX trailer only had a sticker which is totally faded, hopefully I can still get it registered). I will search for the freeze out plug with the serial number.

Yeah I wasn't planning on using chainsaw oil. I just didn't know the specs or best brand to use for an outboard. Thanks for pointing out the oil type I need.

I'm playing it safe with changing the oil first off for safety reasons. Thanks, it's good to know why and when to change the oil in the fall.

When we get a day above freezing (I think this week) I'll shovel around the boat and give the motor a real good look over. Would hate to be stuck floating around because of being stupid and missing a bad wire or what not.

As I do the compression test, should I do a wet one in case the cylinder rusted a bit? Don't want to ruin the rings or score the cylinder walls if they really are in good shape.

 

[racerone]

Picture might identify it in seconds.

 

[jhande]

I'll try to find my wife's old cell phone and snap a few.

 

[jhande]

Here's a few pics my son took. The 3rd pic is on the transom mount tube were the steering cables go into. Still no plate/decal found anywhere else. We even took the cowl off looking for the plug in the block with the nummber stamped in it, no luck can't really see the block.

 

[jhande]

If that is really the serial number in the 3rd pic above...
I found this website https://www.oldmercs.com/category_s/2687.htm
Scrolled down to Models 1977-79 and found
Model: Merc | Horse-power: 50 | Serial Number Range: 4962056 thru 5193258 | Year: 1978.
My number found in pic: 5112288 which falls in that range.
Did I figure it out, hopefully?

 

[racerone]

You found the serial # on that plate.---And the decals also indicate it to be a 78 model.

 

[jhande]

Thank you for confirming.

I couldn't find any info pointing me to where I found that plate so I wasn't sure.

 

[jhande]

Looking for the best repair manual, parts list, owners...
Any suggestions would be appreciated.

 

[racerone]

My advice is always the same.-----Do a complete evaluation of the motor before spending any coins.----Carefully check all wiring.-----Compression test , post the numbers.-----Remove bypass covers to inspect pistons and rings.----Inspect gears, bearings and seals in lower unit.-----Carburetor cleaning and kits would be the last thing to think about.

 

[jhande]

I spent a few hours just looking the motor over with my son (better eye sight LOL). I found a condenser looking part behind the solenoid which has one wire on one end and two on the other. The wires I can trace are attached to a ground. One of those wires the insulation is cracked open and the wire inside is nasty green and crusty. I'll try to get pics today to post.

I do plan on doing some preliminary test before spending any money even on manuals. Was just planning ahead if everything checks out okay.

Right now the weather has been crazy. One day it's 40F the next it's 28F. I'm to old for those cold days, can't handle it much any more.

 

[racerone]

That is a safety switch and not a condenser.----Shuts motor off should you hit a log and motor jumps out of the water.------No need to post pictures of that bad wire , most have seen many examples of bad wiring on this era of Mercury products.

 

[jhande]

That is a safety switch and not a condenser.----Shuts motor off should you hit a log and motor jumps out of the water.------No need to post pictures of that bad wire , most have seen many examples of bad wiring on this era of Mercury products.

WOW never would have guessed that to be a switch. Thank you! Will it be a problem as bad as it is trying to test run the motor? Also, is a replacement available?

Been having trouble finding like break down schematics online that show's such things.