Logo
Get instant online access to repair manuals for your Mercury / Mariner outboard. Online Manuals
MercuryMariner
Order printed Mercury / Mariner service manuals — shipped to your door! Printed Manuals
MercuryMariner
Use engine diagrams to find & order parts for your Mercury / Mariner engine. Engine Diagrams
MercuryMariner
Find parts quickly with Mercury application guides. Quick Parts Guide
MercurySierraCDI
Results 1 to 23 of 23
  1. #1

    Angry 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Hey,

    I am new to the forum and seeking some help with my 50hp Mariner.
    The issue: Took her out a few weeks ago and up on the plane cruising, then with the throttle fully forward the engine cut itself back to almost an idle just leaving us to limp back to the boat ramp.
    Initially I thought it was a fuel delivery issue as the fuel hose was pretty bad with air leaks at most joins, I manufactured a new hose with automotive fuel hose thinking it would be ready for the next weekend!
    Went out the following weekend... something happened and also with the throttle FWD it was surging and back to low revs all the way back. During fault diagnosis I canít replicate the fault under load but it is miss firing at mid throttle.

    Fault diagnosis carried out so far:
    Compression test ✅
    All fuel filters replaced ✅
    Initial fuel pump diaphragm inspection ✅ (havenít put them up to the light but they looked in great condition)
    Spark plugs replaced ✅
    HT leads replaced ✅
    Resistance check of coils ✅
    Isolate each coil while running by removing lead from spark plug ✅
    Stator visual inspection- looked like new ✅
    Stator resistance check ✅
    Timer assembly visual inspection ✅
    Timer assembly resistance check ✅
    Timer Volts checked with Peak voltage adapter ✅ (did drop put that down to magneto pick up)
    Power pack volts with Peak voltage adapter ✅- volts did drop across all cylinders close to misfire!

    I am going to check the fuel pump diaphragms closer and vacuum line to the pump.

    it looks to me to be the power pack but I donít want to spend money on that in case it isnít, in my head it still feels like a fuel issue when driving and it dropped back it felt like the engine was choking.

    Iím not too sure what faults the power pack can cause on the engine, any help on this would be greatly appreciated thanks in advance.

    Martin

  2. #2
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,296

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    You need to clean out the carbs. (That's the first thing you should have done.) With that deteriorating fuel hoses, lots of particles are plugging up the works.

    Jeff

  3. #3

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Will do that first thing Monday...

  4. #4

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Gave the carby’s a thorough clean today and no change ☹️

  5. #5

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I have performed a peak voltage test on the stator today, it is good on the low rev side(blue). When I tested the high rev side (red) the volts were nearly double what’s recommended... It is obviously faulty but can’t think how that is going to give me the issues I have? Could the CDI be bad too? My next thought was head gasket or cracked head, but have been told they are “one piece” and unlikely to be the problem. Anyone have some ideas?
    Cheers

  6. #6
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,296

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    One piece all right. Looks like it's stator time.

    Jeff

  7. #7

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Cheers Jeff

  8. #8

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Changed the stator and timer, new carburettors and used a donor CDI , no change still have a miss at mid revs. The only other things I was think were all 3 coils or the fuel pump? Or just scrap the engine?

  9. #9
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,296

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Don't scrap it! You might have a bad reed valve. I ran into that on one of those I was working on. Pull the carbs and the plate behind them and take a look.

    Jeff

    PS: This is one of the three carb triples, right?

  10. #10
    Join Date
    Sep 2010
    Posts
    17,554

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I think it has 3 carburetors.

  11. #11

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Yep triple carby, will try and find the reef valve

  12. #12

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Reed valve

  13. #13

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I have taken the plate off and can see the valves from the front side, how do I know if they are seating correctly? Do I have to take off the whole unit behind?

  14. #14

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I have them off, didn’t realise they have two plates stacked together

  15. #15

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I have found on number 1 cylinder 3or4 valves with daylight coming through when a torch is held behind it. From first inspection with the ***** eye they look ok but when using light behind it there is definitely a tiny gap, how much deformity does it need to be bad?

  16. #16

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    New reed valves ordered should get them in tomorrow, thought I best had seems I have the unit off

  17. #17
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,296

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Good luck.

    Jeff

  18. #18

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I have changed the reed valves, it seemed to run better the first time I ran it. The second time I am getting the miss again what do you think is the next option going forward?

  19. #19
    Join Date
    Nov 2011
    Location
    tennessee
    Posts
    3,568

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    You should have the model with the big pack with quik-connectors...these can cause a miss also. Best to check spark with timing light when missing to see if it is a cylinder dropping or fuel problem.
    Pappys Sales and Service
    Owner and Factory Certified Technician
    Former racer KDBA (Kentucky Drag Boat Association)

  20. #20

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    I have checked the spark while running with an in-line tester, spark doesn’t drop off when it misses. I have re checked the compression and come out level on al 3 @115psi, I have taken out the spark plugs which are brand new during this fault diagnosis process and #3 cyl was quite badly fouled, #2 had a bit of build up and #1 cyl was clean.

  21. #21

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Is there a way to check the fuel pump without having to replace it?

  22. #22

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Any ideas Jeff?

  23. #23
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,296

    Default Re: 1995 Mariner 50hp 3Cyl Engine cutting back to idle from full throttle

    Just replace it and be done with it being a concern. Not too expensive.

    Jeff

Similar Threads

  1. 92 Seaswirl OMC 5.0 302 Ford Engine Stalls when when given full throttle from idle
    By pgrant1964 in forum OMC Sterndrive and Inboard Forum
    Replies: 1
    Last Post: 08-04-2019, 10:49 PM
  2. 92 50hp Mariner bogging down on full throttle
    By basskidd in forum Mercury Mariner Outboard Forum
    Replies: 2
    Last Post: 08-21-2014, 06:28 AM
  3. 1997 J25 Teleum cutting out at 3/4 to full throttle
    By N4ILZ in forum Johnson Evinrude Outboard Forum
    Replies: 3
    Last Post: 09-10-2012, 08:30 AM
  4. 1985 mercury 50hp 4 cylinder--cutting back at wot
    By nitro901 in forum Mercury Mariner Outboard Forum
    Replies: 10
    Last Post: 10-04-2011, 06:48 AM
  5. 125 hp engine kicks back at full throttle
    By smittyballz in forum Chrysler Force Outboard Archive
    Replies: 3
    Last Post: 07-06-2007, 02:08 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •