Problem starting 1975 Mercury 500

Tanksmydog

Seaman Apprentice
Joined
Jul 8, 2008
Messages
41
Hello,
I am having a problem starting my Merc 500. A week ago I started it up and ran it for 5-10 min with no visible or audible problems at all. I ran the prop forward and reverse with the the motor being flushed the entire time, but just yesterday I tried starting it and it will crank but not fire up. I checked and clean the spark plugs. The starter is turning the flywheel but that is all it would do. I tried using the pull rope to start it but it did not fire. Fly wheel turned with no problems. What could be the problem? I did check to see if the controls were in neutral and they appeared to be so without opening it up. Does it appear to be a cheap easy fix or not? Thanks again helping.
 

Laddies

Banned
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Sep 10, 2004
Messages
12,218
Re: Problem starting 1975 Mercury 500

Cheap or easy aren't in the marine book, first check it for spark if it has spark then use a squirt can and squirt some fuel in the carb to see what happens. It sounds like there is no spark however.
 

Tanksmydog

Seaman Apprentice
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Jul 8, 2008
Messages
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Re: Problem starting 1975 Mercury 500

LOL yeah I know about the cheap easy thing but I thought I would try. JUst curious but if it isn't the spark thing, what else could it be? Thanks.
 

allymoss

Petty Officer 2nd Class
Joined
Feb 3, 2007
Messages
163
Re: Problem starting 1975 Mercury 500

check these things.

spark - if there is, its a fuel problem. If no spark then ignition problem.

If its non of those it could be compression, timing and a number of other small things.

New set of plugs is first thing to do.
I suspect you will find there is a spark and there is dirt in your carb or fuel is not getting through.
 

Tanksmydog

Seaman Apprentice
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Jul 8, 2008
Messages
41
Re: Problem starting 1975 Mercury 500

Ok I changed the spark plugs but still no change. If it is the ignition how easy is it to replace? Rough cost? Would it be something else? Oh yeah how hard is it to clean the carbs?
 

TommyA

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Jun 3, 2008
Messages
148
Re: Problem starting 1975 Mercury 500

Are you getting any spark? If you are unsure how to check for spark it OK to ask. If you remove a spark plug and lay it on any metal part of the engine with the wire still attached, then pull the rope or turn the key and notice if there is a spark at the plug end. You must determine this before doing anything else..
 

Tanksmydog

Seaman Apprentice
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Jul 8, 2008
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Re: Problem starting 1975 Mercury 500

OK, what do I do if NO spark? What do I do if there IS spark?
 

lots of boats

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Jul 28, 2008
Messages
116
Re: Problem starting 1975 Mercury 500

Hi
Yes, check for spark first.

I can't remember if the 1975 merc 500 had a belt driven magneto, or a CDI box. I think it was CDI.

If it has no spark and a CDI box the two places that were common causes of spark failure were the key swich and the tilt kill switch. I think that both had black yellow stripe wires.

CDI boxes didn't ususally die when not in use.

If there is no spark disconnect these black yellow stripe kill switch wires from the CDI box, they usually went to the bottom stud, and then crank the engine with the plugs in the caps. Careful you don't start a fire, or zap yourself.

If it has a belt driven mag, clean it.

Cheers
 

Tanksmydog

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Jul 8, 2008
Messages
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Re: Problem starting 1975 Mercury 500

OK I have spark but it is still not firing up. If it would happen to be the carbs, I need detailed instructions w/pictures to clean them. Either way, I will need instructions w/pictures to fix my outboard. What might be going on with my motor? Please Help!!! If you live in Northeast Ohio and could come over and help me I would be extremel grateful.
 

lots of boats

Petty Officer 2nd Class
Joined
Jul 28, 2008
Messages
116
Re: Problem starting 1975 Mercury 500

Hi
You could tell us a little bit more about the motor, and in the process take a good look at the options to make it run. Does this motor have open throat carbs, you can see in, two carbs, 4 cylinders, a blue plastic cover on the fuel screen on the side of the carbs, and you can't easily get the screen off the bottom carb? If this is your motor and you have a nice fat blue spark, and you have water in the block and you are wetting the water pump, and you have a fire extinguisher, then take a can of WD40 and spray it straight into the clylinders as you crank the engine, with the plugs in. If that doesn't burn then try some oily gas straight into the clylinders. If you can get it to fire then clean out the fuel system and replace the fuel pump diaphram gaskets etc. Have fun.
 

tredragon

Petty Officer 2nd Class
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Jul 2, 2008
Messages
122
Re: Problem starting 1975 Mercury 500

do you have a bulb on the fuel line that you prime with? try pumping it quite a bit and make sure it stays hard after. When you take the wraparound cover off (the one that wraps all the way around the upper unit of the engine), if you look from the boat, backwards, you will see two 1" diameter holes, those are your carbs. Squirt a small shot of gas in there and see what happens. If it wants to fire then, you're not getting fuel to the carbs. You need to follow the hoses that go from carbs all the way to the tank, checking each "stop" along the route. You have a fuel pump diaphragm that may have gone out...

It really could be a number of things and I'm by NO means an expert. It may be that you're slightly in over your head. Finding an old salt or going to the mechanic might be your only option if troubleshooting it doesn't prove to work and you have to have it fixed now.
 

Tanksmydog

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Jul 8, 2008
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Re: Problem starting 1975 Mercury 500

any websites with pictures and/or diagrams?
 

TommyA

Petty Officer 2nd Class
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Jun 3, 2008
Messages
148
Re: Problem starting 1975 Mercury 500

I don't believe that anyone here can help you with your problem. My suggestion is to take it to a qualified mechanic who can do the troubleshooting on your engine.
 

Moody Blue

Captain
Joined
May 24, 2004
Messages
3,136
Re: Problem starting 1975 Mercury 500

Would highly recommend a proper service manual. Best investment you can make if you own an outboard.

Trying to fix such a problem on-line is very difficult and time consuming to do. Must be very methodical and logical in the trouble shooting process or else you just end up chasing phantom problems without identifying the real one.

A bit of background info is helpful. What year of motor? Is it new to you or have you owned it for awhile? Have to ask, are you familiar with the correct procedure for starting the motor?

In the first post, why did you try starting with a rope? Was the starter not working properly?

Confirming you do have spark at each cylinder?

Do you have a kill switch hooked up to your motor?
 

Tanksmydog

Seaman Apprentice
Joined
Jul 8, 2008
Messages
41
Re: Problem starting 1975 Mercury 500

I just tried to take out the fuel filter, one of them, cleaned around it and though it wasnt the best job the motor fired up. Now I need to replace the filters, but am havin trouble figuring out how to do that. I have a seloc online manual but am new to it. Please help also I do not know what carb I have there are 4 choices for this year according to the manual.
 

kingsnakejr

Seaman
Joined
Jun 16, 2008
Messages
70
Re: Problem starting 1975 Mercury 500

What's your serial number? Maybe we could look up your carb for you.
 
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