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  1. #1
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    1981 50HP Merc not running at full power. Please help

    I just recently had a coil go out on my 50HP Mercury. I got a brand new coil and put it in and now have lost around 10MPH at full throttle. I have also rebuilt both carbs and changed the plugs but no improvement. My thought is the new coil is bad. Is this possible? I hate to spend another $50 on a coil just to see if the top end speed improves.

    I am past the return date on the coil being it took me all summer to trouble shoot the problem. I first thought it was a carb, then the coil, back to the other carb and then finally the coil. The problem was so infrequent that it took all summer to pinpoint it. When I put the old coil back in the motor runs great for about 30 seconds then goes to running bad again. So it has to be the new coil, right?

    This is what I have done. I have checked all the wiring and it is looking tip top, I tightened a few loose wires so good to go. I checked spark on each cylinder and have good blue spark coming from the plugs. I decided to check the compression and have 120 on each cylinder. I checked the wires on the stator and all look good. Does anyone else have an idea on what to check? I am still not at full power and the only thing I can think is trying another coil.

    Fuel lines are new, both carbs are brand new. I have new clean fuel, good spark, good wiring, and good compression. I am at a loss, any help or thoughts is appreciated.

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  3. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #2

    Re: 1981 50HP Merc not running at full power. Please help (biscuits)

    Reeds inspected?




    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

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    #3

    Re: 1981 50HP Merc not running at full power. Please help (EuropeanAM)

    I am not sure what the reeds are? can you point me in the right direction?

  5. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #4

    Re: 1981 50HP Merc not running at full power. Please help (biscuits)

    I'd recommend looking up the Crankshaft Section of the Parts Diaghrams on our website (via engine serial number if possible):

    http://www.mercurypartsexpress...arine

    You're looking for the reeds that are attached to two (2) Main Bearing assemblies.

    These reeds provide the sealing action that ensures fuel and air are properly drawn into the engine, at the correct times. If broken or missing.... you may have good compression, good spark, plenty of fuel with good carbs- but little or not "actual combustion power" being produced on the affected cylinder(s).




    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  6. Member
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    #5

    Re: 1981 50HP Merc not running at full power. Please help (EuropeanAM)

    I did some looking today and I beileve I can check out the reeds on my own. It looks as if it is a faily simple job but I want to check with you to be sure of a few things before I start this project. By the way the serial number is 6012738 if that helps.

    I believe I need to drop the lower unit in case I need the crankshaft to move a little, take off the crankcase assembly/head and the reeds will then be in plane view because the crankshaft and reeds will be at the top.

    Am I looking for excessive wear on one of the reeds? Will the damaged one be obvious?

    Would you recommend changing all the reeds since I have it apart or just one? I assume there are four reeds, one for each cylinder so hoping just replacing the damaged one(s) will work ($60 each) yikes!

    And what else would you recommend I change while I have it apart? Gaskets or any bolts?

    Once I get it back together will I need to reset the timing?

    Last question is before I tear this motor down and inspect the reeds is there anything else I should try to look at?

    Thanks in advance and I will let you know how it goes. From your web page it looks like you have the parts so look for a call from Texas in the next week or two.

  7. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #6

    Re: 1981 50HP Merc not running at full power. Please help (biscuits)

    First... let me point out that it's been a few years since I tore too far into one of these. Well actually... more than a few.

    As I recall- if the carbs are removed, and you look down through the intake "just right", you can actually see portions (but not all) of the reeds without complete disassembly (might be worth a look.... at least you might feel better tearing into it).

    If you were to pull the powerhead, and remove the crankcase front-half, you'd certainly have a pretty good view of the reeds. You're primarily looking for reeds that are bent open, chipped, cracked, or have pieces/petals MISSING.

    Certainly replace ANY that are damaged. If I were going the the trouble to pull it down that far- I'd be inclined to replace ALL of them (you'll need TWO reed kits).

    You'll also need appropriate sealant for the crankcase halves, carb gaskets, powerhead gasket, etc.

    After complete reassembly, a Sync-n-Link proceedure must be completed (as described in the Service Manual).




    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

  8. Member
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    #7

    Re: 1981 50HP Merc not running at full power. Please help (EuropeanAM)

    I had a look at the reeds and both look fine as far as I can tell so I went ahead and bought a new coil just for curiosity sake. I dropped the boat in the lake, fired it up, idled out, gave it full throttle and nothing. Hahahahahahahahaha this is driving me crazy. The new coil is worse the the other new coil. I could not even get on plane.

    So here are my thoughts and maybe you can give my your opinion. I believe it is a ignition/eletrical problem. I looked over the wiring and all looks good but perhaps it is not. So is there a way to test the stator and trigger? Could it be the control box and if so is there a way to test it? Replacing the control box is $200+ and the stator is $150. I hate to throw parts at it when the cost is so high. Any thoughts? If I was going to throw parts at it I would try the stator first but I sure would like to know if there is a way to test both first.

  9. Mercury - 3 Liter Moderator EuropeanAM's Avatar
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    #8

    Re: 1981 50HP Merc not running at full power. Please help (biscuits)

    If you have a service manual for your engine, testing methods are listed/shown for both the stator and the trigger.

    Run through the RESISTANCE tests on the stator FIRST. You may have one winding that's failing. Then, perform the DVA tests (a DVA, or Direct Voltage Adapter is required).

    On the TRIGGER (please read CAREFULLY): Peform the RESISTANCE TESTS on each paid of wires. WHILE TESTING each pair, have someone move the throttle from IDLE to WOT position and back while you watch the readings. There should be NO substantial fluctuation in the readings!

    If you note substantial fluctuations in the stator readings as the throttle is moved, it's highly likely that there is a break in the trigger's wiring harness (requiring replacement of the trigger). This particular problem is almost impossible to diagnose... but throttle movement while testing may allow you to "perceive" that the problem exists.




    Dual Mercury Master Technician- for Mercury Outboards, Racing & Mercruiser Sterndrives in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 38 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor

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