Mercury 50hp 2stroke 4cyl 1984?

Miragut

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Sep 19, 2017
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I believe what i have is an 1984 mercury, not to sure about model. Serial number on frame is 7212144, havnt found out much online from the serial number. Would like any information someone can provide me with, first outboard motor owned. Turns over no problem but not starting. Basically looking for some help with the year and most common problems.

I checked gas flow, fine
Compression is fine
New marine battery
Spark is the next thing, new plugs but its not smoking at all, going to test that tonight
 

nipperdog

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Sep 12, 2017
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Do you have a spark gap tester? It's a little clip looking deal with a spark plug type connection on one end, and an adjustable gap with a clip on the other end to attach to the motor. This will allow you to properly test the spark voltage and current available. They even make one with four connections so you can test alll 4 cylinders at once, but the single version is very affordable, like a few bucks. Second best for checking spark is holding a connected plug against the motor head and spinning it over, watching for a nice blue hot spark. You want to check each cylinder, and don't jump too much if you get shocked a bit. :) If you have spark on all 4 cylinders, you can spray a mix of gas/oil just like what's in the tank, down the carbs as you try to start it. If it fires up and dies this way, you probably have fuel pump/carb. issues. That will get you started, and hopefully someone more knowledgeable will chime in, in the time being. I'm just a shade tree guy since I retired from pipefitting a couple years back. Good Luck!
 

stikboyy

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1984 MERCURY 50 EL model #
1050524.

In order for a motor to start you need 3 things: Spark, fuel, and compression. Check all cylinders for compression; as long as the numbers are 90 psi+ and within 15% off the highest number your motor should run decent. nipperdog explained how to check the spark and fuel side. Hopefully this gets you on the water!
 

Miragut

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Weird thing is the plugs i have are ngk BUHW and there is no curved peice of grounding electrode, these ones are just flat at the end which is wierd are these ones okay? Or should i get the buhw-2 ones that have the gap?

Thanks for the help!
 

stikboyy

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Mercury calls for BUHW-2 spark plugs in your motor. They are still flat on the end. This type of spark plug is called a 'surface gap' plug and your motor is designed to run this type of plug.
 

Miragut

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Mercury calls for BUHW-2 spark plugs in your motor. They are still flat on the end. This type of spark plug is called a 'surface gap' plug and your motor is designed to run this type of plug.

Iv also heard of plugs with a resistor in it made by ngk .BUZHW-2 are they any good or should I move on from the BUHW to the BUHW-2?, this is te first time iv seen a flat surfaced plug with no ground post at the end
 

nipperdog

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The flat surface plugs work very well in my limited experience, and are very difficult to foul. I put a set through spark plug heck and they survived fine. I don't think they would be giving you any trouble. I think Mercury even had a special name for them, like perma-gap or something similar. One thing of note, is the plug wires on these older motors are real wire inside, not the graphite like stuff in modern wires. I think this may be important when replacing wires as the new style can offer resistances of 84k ohms or even more. Not sure the older ignition systems are up to the task of dealing with all that resistance? As said earlier; fuel, compression, and a good spark at the correct time and the motor will at least "run". Let these guys know you have done the suggested things, and they will go from there. Until that, they can't even guess.
 

Miragut

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So changed 4 plugs to the BUZHW-2, tested for spark and nothing on all 4 plugs:( theres not really any corrosion visible on the connections from battery to starter,
Any chance i can test with a multimeter or ohms reader?
 
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