1986 Mercury 45 HP CLassic Fifty ignition problems?

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Aug 6, 2012
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IMG_0716.jpg In the last six years I have replaced the ignition module twice. This motor will run great when I first start it but, after 10 minutes or sometimes 6 hours, it will start giving me problems. I may be blasting across the lake at full throttle suddenly it will run as if 3 of 4 plugs are fouled out or not getting any fuel? I can let it cool off (not that it is overheating) and it may start working right after 1-2 hours. I know it is getting fuel. Any suggestions?
1986 Mercury 45 HP classic Fifty s/n 0A999270 ..... Any help would be appreciated.
 

Georgesalmon

Lieutenant Commander
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Apr 14, 2012
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1,793
Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

Got a fuel/water seperator?
 
Joined
Aug 6, 2012
Messages
6
Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

Has new gas tanks and fuel lines. Carbs have been cleaned and checked. Burning 92 octane with Merc mixing oil.
 
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Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

Still looking for that Merc Expert to point me in the right direction.....
 
M

Maxz695

Guest
Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

Your electrical looks to be in good condition from what I can see the thing is the things you can,t see. The flywheel may have to come off and inspect the trigger and the stator wires (especially where they come out of the stator) These sometimes wear on the block or endcap stator bracket and the insulation becomes worn which can cause intermintent grounding and severe ignition failure (SWITCHBOX). just a thought
 

CharlieB

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Apr 10, 2007
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5,617
Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

An old saying, "If it ain't broke....."

When the condition occurs you have to immediately test a couple of things to determine where the problem is.

Take a spark plug wrench, another set of plugs, and a spark tester along.

As soon as the motor starts running foul, remove the spark plugs and inspect them closely, you are looking for either a carbon fouled plugs or gas soaked fuel fouled flooded plugs.

Ground all the plug wires then test each one at a time for a hot blue arc across a 7/16 inch gap.

Hopefully this will clearly show the ignition system to be good or bad and also give you a good idea if the fuel system is flooding one or more cyls.

If the ignition is good, screw in the new plugs and order carb rebuild kits.

If any plug wire fails to pass the spark test then further testing is necessary to determine which component of the ignition is at fault.

Always remember, with any electrical part, do NOT assume anything, there is NO RETURN on electrical parts. You must test and prove any fault before even thinking of replacing anything other than the spark plugs.
 

quicktach

Petty Officer 1st Class
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Aug 24, 2012
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394
Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

Why did you replace the ignition modules ? It appears that replacing them gets the motor running again. So you should try to find out what's making the modules act up and fail. Clean all grounds and look for shorting wires. I'd pull the flywheel and look under it at the trigger coil and the stator coil. Is the stator coil secure? Does the trigger coil move freely? Any wires damaged. Is the trigger coil wiring restricted in it's movement? Is all linkage to the trigger coil freely moving? Check coils with DVA equipped meter. Any signs of overheating of coils or wiring? Check the entire wiring system carefully. Something seems to be interfering with the correct operation of the CDI.
 

CharlieB

Vice Admiral
Joined
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5,617
Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

One thing that will kill a switchbox is any voltage feeding thru the ignition switch into the Black w/Yellow trace kill wire. Any errant voltage passing thru the ignition switch to the switchbox will kill that switchbox.

But here again, you cannot ASSUME anything as there is NO RETURN on electrical parts.

If it is suspected the ignition switch may be contributing to early switchbox failure then the ignition switch should be tested, simply disconnect the Back w/Yellow trace wire from the ignition switch and connect a volt meter to that terminal of the switch, turn the key ON/OFF while watching the meter for ANY voltage no matter how slight. You may have to cycle the switch sixty or a hundred times to be CERTAIN of your findings. You may also want to disconnect the starter wire from the switch so you can fully turn the switch all the way to the start position to fully duplicate full switch movement.

Intermittent electrical problems can be some of THE toughest nuts to crack. Often soled only with patience and enduring testing.

Simple part replacement rarely solves a problem until most every component has been replaced, at serious expense.
 
Joined
Aug 6, 2012
Messages
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Re: 1986 Mercury 45 HP CLassic Fifty ignition problems?

Thanks, This makes sense and at least something worth looking into. I carried this motor to two different "Professionals" who said it was the electronic ignition module the last two times when it was changed. This may have been a symptom of the problem but, not the problem.
 
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