1984 Mercury 25 xd starting promblems. Please help

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TimFromSaintCloud

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Jan 19, 2013
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Hello I have a 84 mercury 25xd. Had it for 5 years with no promblems. Yesterday it wouldnt fire up at all. Today a went to test the spark and the bottom was fine. Then I tested the top and it kinda back fired and smoke came out of the propeller. ??? The only work Ive dont to it over the years was new plugs,wires, and coils. It never sits for long periods of time, Im in Fl and use it 2-3 times a month all year long. Any help would be nice. Thanks
 
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oldman570

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Re: 1984 Mercury 25 xd starting promblems. Please help

There are several things that could cause the motor to not fire and then pop thru the exhaust while testing for spark. Bad plug, plug wire, coil ground, coil going open, bad switchbox, triger going bad just to name a few. Check all connections for good contact and switch the plugs around to see if it moves with the plug. If it moves then the plug is bad. Start with the easy tests first and work back to the flywheel and triggers as you go. Parts for the motor are fairly easy to get, but some are getting costly. Being your in a salt water inviorment , the connections are probly the trouble. JMO
Oldman570
 
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Maxz695

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Re: 1984 Mercury 25 xd starting promblems. Please help

I,m in florida and agree salt water does a number on electronics. Loosen and retighten all connections. Check grounds and wire insulations. Pull the plugs and swap as stated by Oldman570 or replace them. Unplug coil wires, and plug wires, as build up may be creating a barrier. How old is the fuel and did you try to shake or mix it before starting the engine? It may be the oil settled and was not properly mixed last fueld and is sucking mostly oil. Just a few thing to look at and try. Please get back to us if things don,t improve. Good luck
 
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TimFromSaintCloud

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Re: 1984 Mercury 25 xd starting promblems. Please help

Ok.. I did check and clean all the connections, I only run in fresh water so they were pretty easy to clean. I changed the gas out with fresh. I can see that the carb is getting gas, and the gas is getting to the plugs. I took off the coils and cleaned everything, took the plug wires off and re connected. The spark plugs are only 3 months old so I didnt change them. Still no luck. Im gonna have to research to see how to test the trigger/ switch box. Thanks for some tips
 
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oldman570

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Re: 1984 Mercury 25 xd starting promblems. Please help

You might have a bad fuel pump also if it has not been rebuilt latley. You can spray some mixed fuel in the carb and see if it will start and run then. Also check the fuel filter to see if it is pluged. If you are using the 10 percent gas of today the fuel hoses will deterate and some particals of the hose will plug up the carb passages. Just a thought, as the fuel pump can allow fuel to leak into the crankcase and cause a flooding of the motor. JMO
Oldman570
 
quicktach

quicktach

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Aug 24, 2012
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Re: 1984 Mercury 25 xd starting promblems. Please help

Sounds like an electrical problem. Check entire electrical system as others have advised. You can test the stator and the trigger initially at the connections (opened) to the CDI. You can use a VOM to measure the resistance on the coils initially. Could be problems under the flywheel too ...damaged wires, bad magnets, rust, loose connections, trigger plate damaged. Try checking all else before removing flywheel. If stator, trigger, plug coils, wiring, grounds check out ok ...then by default it's probably a bad CDI.
 
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ANFAC76

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Re: 1984 Mercury 25 xd starting promblems. Please help

I?ve had that problem not long ago. One of the sparks was fine and the other one not. The failure was located at the flywheeler magnets, they were loose. I could displaced them with my finger. I took off the flywheeler, and stuck them back again at their initial possition.

If the magnets are fine this is what I would do.

1.- Swap the coils and see if you get good spark. Both unplugged and grounded. Best at dusk.
2.- Swap the ground black wire that goes from the cdi box to the coils.
3.- Measure the ohms on the coils. And post the readings. Between negative and pipe, and negative and possitive.







TimFromSaintCloud said:
Hello I have a 84 mercury 25xd. Had it for 5 years with no promblems. Yesterday it wouldnt fire up at all. Today a went to test the spark and the bottom was fine. Then I tested the top and it kinda back fired and smoke came out of the propeller. ??? The only work Ive dont to it over the years was new plugs,wires, and coils. It never sits for long periods of time, Im in Fl and use it 2-3 times a month all year long. Any help would be nice. Thanks
Click to expand...
 
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Cspez

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Mar 3, 2013
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Re: 1984 Mercury 25 xd starting promblems. Please help

Hello, everyone

I have the same 1984 mercury 25xd and can not find the correct trim tab anode. The top of the anod that goes into the bottom of the trim tab above the propeller is a wedge looking opening the is tapered and gets wider moving closer toward the Boat. The anodes that I find are for newer 25 hp mercurys have a different shaped bit that is round wher the anode bolts in and will not fit I may be able to grind it down but would rather fing the correct anode. Does any one know where to look?

Than you
 
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