merc 25 sounding odd *help*

Discussion in 'Outboard Maintenance' started by HighSide25, Dec 2, 2008.

  1. HighSide25

    HighSide25 Well-Known Member

    i have been running my motor a lot this past week and it sounds like it is having some serious nocking or cyl. slap between about 1800-3000 rpm's. almost like the fywheel is barely catching on a little ratchet. anyone have any idea of what it could be? i seafoamed it to try and fix it, but to no avail. could it be the carb?
  2. iMacattack

    iMacattack busy, too busy

    in gear or in neutral? I would not run it if it were me. Without seeing/hearing it you might have a burnt bearing on the rods. I would seek professional help.

  3. Brett

    Brett > PRO STAFF <

    Had a similar occurence, electronic modules on stator plate
    under the flywheel were shifting position and were making
    contact with the flywheel.
  4. Flyline

    Flyline Won &quot;Do More With Less&quot; Award!

    I post this section for 2003 merc 25hp 2-stroke been acting up and thought my carburator kits will solve the issue but this is not it. Find out one of my compression test is low and piston rings is fried around the piston.

    This merc 25hp 2-stroke needs rebuilt powerhead, new pisions, rings,gasket and valves after been running hard 500 hours of use.
  5. HighSide25

    HighSide25 Well-Known Member

    brett, im thinking its close to what happend to you, how did you fix it?
  6. Brett

    Brett > PRO STAFF <

    Got a shop manual for my motor.
    Got a big piece of cardboard.
    Took pictures of the existing engine as I disassembled, step by step.
    A part removed was taped to the cardboard and numbered.
    Accessed the flywheel, removed it, and took more pics.
    The sensor and alternator coils had vibrated loose and were
    making contact with the flywheel. Bright metal showed where.
    Stator plate was ok, bought new electrical parts and installed
    per instructions in shop manual. Clearances are important.
    Reassembled engine reversing the numbering sequence from my
    cardboard parts board. Followed correct torque specs per the manual.
    Once reassembled, checked and adjusted the timing per the manual.

    If you are going to do your own work, start with a compression test.
    Easy to do, and it'll let you know how your engine is wearing.
  7. B.Lee

    B.Lee Well-Known Member

    I've seen that happen to these motors (and others) before too. Do a compression test first to be sure there is nothing detrimental going on.

    Pulling the flywheel is fairly simple. If there is anything loose and rubbing, you'll know it then.
  8. HighSide25

    HighSide25 Well-Known Member

    problem solved.
    i took off the do-hicky, sprayed some oil, took off a little bit of rusty areas on the do-hicky. good to go, no more pinging.(i thnk it was something near the man. starter/rope gizmo. i also rented a compresion tester thinger majigger. anyone know how to hook those up? i tried and it wont stay up(story of my life ;D), do both plugs have to be out? highest psi i could read was like 60 on both, i know thats low, i think the reading is off because the motor runs awesome
  9. iMacattack

    iMacattack busy, too busy

    Start and warm the engine up to operating temperature. Shut down and remove all the plugs. Put the gauge with correct threaded adapter to fit your spark plug hole into the first cylinder you're going to check. Turn the key or pull the rope and crank the engine over several times. Record the pressure and go on to the next cylinder. All cylinders should be within 15 lbs of each other. Good luck. And let us know what the results are.

    Capt. Jan
  10. futch13

    futch13 Well-Known Member

    Valve on tester is stuck open or not installed. Looks like valve stem on tire
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