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  1. #1

    Default 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Hello, I am new to the forum.
    I have a 1986 Mercury 50hp outboard motor (ser# 08a996688) and am experiencing an odd problem.
    Motor ran great last season and now will not run when trimmed down. Great blue spark on all cylinders when tilted in full up position. But, engine dies and fire is gone on all four cylinders and spark plugs.

    Engine dies at approximately have the way down when trimming.

    I have checked kill switch, fuel flow is great, brand new spark plugs, stator, trigger, fuel lines, carburetors have been cleaned, new floats and needles. Spark plug wires have great spark and continuity when in up position. Coil spark shocked the tar out of me twice by accident. Silenoid fires well.

    As far as I can tell the switchbox is good. But, I am not absolutely sure. Installed a brand new one 5 years ago.

    I have attempted to troubleshoot using a lot of expert suggestions here on this forum. But, not an expert with ohms testing and do not have a DVA adapter.

    I completed the following to the best of my ability: trigger test, stator test, removed the black/yellow tracer kill wire at the switch box.

    I have looked tirelessly to determine if any wires are grounding out or moving when tilting down to no avail.

    I am posting here out of frustration and exhaustion. Ready to get my boat out on the water but, cannot head down the lake with the engine tilted up all the time. hahahahaha.

    Engine runs well, accelerates and seems fine when tilted up. Starts on first crank and keeps running at idle, no problem.

    Any help or suggestions are greatly appreciated.

    Thanks, perry_merc
    Last edited by perry_merc; 03-16-2018 at 09:28 PM.

  2. #2
    Join Date
    Sep 2010
    Location
    ontario
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    14,945

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Have you adjusted low speed mixture needles, yes or no ?----Compression test done ?----Exhaust checked for blockage ?

  3. #3

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Quote Originally Posted by racerone View Post
    Have you adjusted low speed mixture needles, yes or no ?----Compression test done ?----Exhaust checked for blockage ?
    I have not adjusted low speed mixture needles. I have done a compression test but, will do another tomorrow morning, I am in Texas. I will also check the exhaust for any blockage and provide an update.

    Thank you so much raceone.

  4. #4

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    If you have an effective killswitch (mercury switch) on the motor, it shouldn't start in the up position. That is what they are for. I would start there.

  5. #5
    Join Date
    Dec 2015
    Location
    maplevalley WA
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    4,743

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    There is a tilt switch that goes to the switchbox are you disconnecting both wires going to the black/yellow terminal on the switchbox? Sounds like the tilt micro switch to me?
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  6. #6

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    exhaust has good pressure while running and i found no blockage.
    pressure test is good on all cylinders. cyl1-115,cyl2-120,cyl3-120,cyl4-120.
    thanks for all the responses.
    I am stepping through the manual and testing all componenets fro battery, stator, rectifier, stator once again to make sure all is clean and operational.

    i only located one black wire with yellow strip going to switchbox. i will keep searching.

  7. #7

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Seems fuddyduddy and kimcrwbr1 have a great point. The engine runs and starts well in the tilted position, once I lower engine approximately 20%, engine stops and there is no spark. Something is killing the engine when trimming down.

    I have disconnected the black/yellow wire from switchbox and the mercury switch above the silenoid. The mercury switch is mounted at an angle and is the size of a capacitor.

    I am still unable to start the engine in trimmed position when both wires are disconnected.

    I attempted to upload two images. Hope it worked. First timer and all.

    Thank you for the help and responses.
    Last edited by perry_merc; 03-17-2018 at 10:06 PM. Reason: add images

  8. #8

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    I also attempted to start engine in down position with only the mercury switch unwired. Engine would not start in trimmed down position.

  9. #9

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    are you sure its spark? are your carbs flooding over?

  10. #10

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    hello channelcat, i am sure it is electrical. Once I lower the engine a little from full tilt up, spark goes away. I just rebuilt the carburetors and replaced the floats and needles to be sure.

  11. #11

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Is there a way to bypass the tilt mercury switch?. Seems this switch is working in reverse function and grounding out my engine when in trim (down) position versus tilt (up).

  12. #12
    Join Date
    Dec 2015
    Location
    maplevalley WA
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    It kinna sounds like someone messed with it to run in the tilted up position probably for shallow water or to drive the boat onto the trailer. Can you adjust the position of the switch?
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  13. #13
    Join Date
    Dec 2015
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    The mercury switch keeps the engine from running away if the prop gets kicked out of the water from hitting a deadhead while running WOT. It rarely if ever is actually used. Your call if you want to just disconnect it.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  14. #14

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Does not seem to be the trim Mercury switch. Yesterday troubleshooting, I rotated the mercury switch different ways and the engine still would not start trimmed down. No spark lowered 20% from full tilt(up) position. I traced the black/yellow striped wires and made sure there were no bare wires or deteriorated insulation and the wiring bundle looks ok. The mercury switch is back in place.
    I also verified all wiring on the external trim/tilt motor look good on the solenoids and harness.
    This is a new problem, engine ran well last season.
    I have exhausted my troubleshooting steps and do not know what to check next.
    Symptoms are: Engine runs very well in full tilt(up) position, trim down approximately 20% and engine dies, i check for spark, first turnover, there is spark and then no spark to the plugs at all until i tilt up the motor a little and it starts right up.
    I’m not giving up, will be back out there today. Could really use you guys on my team. Any suggestions are appreciated. Thank you.

  15. #15
    Join Date
    Dec 2015
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    maplevalley WA
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    If it works properly with the mercury switch disconnected it cannot be anything else.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  16. #16

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    That would be too easy kimcrwbr1. I have already tried to disconnect the two black/yellow striped wires from mercury switch and the switchbox. That made no difference. I know this is odd and i will try the same today. I will disconnect mercury switch and try to recreate. Then, I will disconnect both wires and try to recreate the issue. This means, start engine in down position and see if engine will start in tilted(full up) position with wires disconnected.

    The first time I tried this, was unable to start the engine when in down trim position.

    That is my one simple goal, to get the engine started and running in trimmed position. Help....

  17. #17
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Do yourself a favor: Don't just see if it will start in those positions, check it for spark. You could be tricking yourself with fouled plugs or dry carbs.

    Jeff

  18. #18

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    yes, very good point. i keep a spark tester between plug wire and spark plug to make sure i see a spark.

  19. #19

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Have you checked to see if the wiring harness is binding up or being pulled on.

  20. #20

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    thank you flyingscott. yes, i have checked the wiring thoroughly from end, back to harness and out the engine compartment. The main reason was to check for any worn insulation or grounds. I also checked for any binding or stress.
    Today I disconnected the mercury switch and the black/yellow stripe from switchbox and tested for spark. Interesting result, there is a strong fire on the first rotation which goes away from there. Stop turning over, wait a few seconds, turnover the engine and the same occurs, first rotation is a strong spark. Then goes away and nothing for remainder of rotations for turnover.

    I tried with just the mercury switch disconnected. Then with both disconnected, no change in symptoms.

    I expect this is normal but, with mercury switch and black/yellow stripe disconnected, lifted the motor in full tilt and still get a strong spark.

    Engine still will not start in lowered position.

    Any suggestions are appreciated. Thanks for the responses.

    Weather is beautiful here and the fish are biting. Crappie and striped bass are running. Stripers are also biting and I bought a new DI Hummingbird.

    I’m going crazy over here.

  21. #21
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Be sure and post the resolution definately a new one.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  22. #22
    Join Date
    Sep 2003
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    You MIGHT have a bad stator. Its only purpose is to provide the juice to operate the ignition. It can be tested at cranking speed with a DVA meter. A dealer should be able to do this fairly easily (and cheaply) if you can't borrow one.

    Jeff

  23. #23

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    I don’t have a trim motor on my boat so don’t know much about them just to be honest but is there any chance water got into electrical components while is was not used from last year? That is creating a short, when engine is lowered water moves and touches something? Just idea always start with the simplest problem. Worked when put away the didn’t when got out something changed while it was not in use just have figure out what changed. Good Luck

  24. #24

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    thank you for the replies. I just went through all electrical connections, cleaned, sanded and used a wire brush. Made sure all wires are in good condition.

    Tomorrow I plan to check all ignition parts: stator, trigger and switchbox. I found a great post (I think it may be fastjeff’s post), I will use this post and my repair manual to thoroughly go through and verify all ignition is healthy.

    I tested this recently but, have learned a lot more from help with this forum.

    Thanks again, will let you know tomorrow.

  25. #25
    Join Date
    Dec 2015
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Have you tried jumping the starter directly from the battery when it dont start? It is possible the battery cable is corroded under the insulation just take a set of jumper wires and when it dont start connect the neg lead to the block next to the starter and just touch the post on the starter with the pos lead. A weak cable could give you those symptoms the cable or connector will get hot where the resistance is.
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  26. #26
    Join Date
    Dec 2015
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    maplevalley WA
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Is there any breaks in the insulation/shielding on the harness where it connects to the engine from the battery?
    It takes a nickle to go first class!
    If it aint broke dont fix it!!

  27. #27
    Join Date
    Apr 2015
    Location
    UK Bracknell Berks
    Posts
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    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Quote Originally Posted by kimcrwbr1 View Post
    Is there any breaks in the insulation/shielding on the harness where it connects to the engine from the battery?
    One other point, has someone fitted a tilt level sender unit, as if they have, that could be going down to ground when tiled down.

  28. #28

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Troubleshooting today is leading to stator.
    I removed the flywheel and visually inspected everything. All looks good but, testing the stator shows it is tired and done.

    blue -> blue/wht wire, 1.3ohms
    red -> red/wht wire, .072 ohms
    blue -> ground, open
    red -> ground, open

    I have a stator on the way and will let you know the outcome.

    I pray this works.

    Thanks again for all the interest.

  29. #29

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    Hello Crew, Latest update is brand new stator and small changes.

    Now I have no spark at all in up or down position with mercury tilt switch connected.

    I remove both mercury switch wires (black/yellow) to switchbox and mercury tilt switch, I have a strong spark in up position but, only one single spark in down position. Engine sparks one time for first rotation and then nothing for rest of engine rotations. The one spark is a good strong spark. And the one spark only occurs if I wait about 5 seconds before turning over the engine. If I turn over immediately, no spark.

    With only the black/yellow stripe mercury tilt switch wire disconnected and leaving the black/yellow wire connected to switch box, no spark at all.
    Last edited by perry_merc; 03-29-2018 at 09:59 PM.

  30. #30
    Join Date
    Apr 2015
    Location
    UK Bracknell Berks
    Posts
    50

    Default Re: 1986 Mercury 50hp, no spark in full down position. Runs when tilted up.

    What is the serial number of your merc or do you have the link to the wiring diagram?

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