Mercury 25hp 2 stroke intermittent issues.

Discussion in 'Outboard Maintenance' started by Miami_Chris, May 15, 2014.

  1. Miami_Chris

    Miami_Chris I Love!

    Sup guys, I am posting this here, as it seems lots of guys on here are running or have run this motor at one time or another.

    It's a 2005 25hp 2 stroke merc that has been giving me issues from time to time. She was up and running perfect a while back after I put bunch of money in for new steering cables, throttle, starter, fuel filter, carb rebuild etc. I used her quite a bit, but unfortunately, life got in the way, and she sat for a long while (still started her up from time to time). Have taken it out a couple times in recent weeks, and at times it has given me issues. It starts up first turn of the key every time, but sometimes in neutral it sounds a bit funny, almost like it knocks, but never dies out. Other times it sounds perfect, and all appears to be well. Another issue is when put into gear, as I push down on the throttle the engine doesn't really seem to respond well and runs as if I am not applying any throttle, when all of a sudden it fires and kicks into gear, and knocks me back on my ass and runs perfect. Some times the issue will come back, some times it won't at all ( first trip on the lake, no issues at all running for a couple hours, last trip run around fishing all day, and engine started to knock a bit idling up a creek at the end of the day, couldn't go very fast back to the ramp because it was windy as hell, but I am sure the throttle up issue was happening as well). I make take it out again tomorrow at the lake to see if the same issues happen again, but I don't want to damage the motor.

    I just typed a whole bunch, and hope it actually makes sense haha, but how about some opinions on what it could be? Carb issue? Electrical? I am leaning towards electrical, as it only happens from time to time, and it kicks in powerfully to running right, but sometimes returns to running rough. Do carb issues happen intermittently like this, or am I right by thinking electrical? Carb, and the two ignition coils are easy fixes, but I am worried it could possibly be the trigger assembly, bad stator, or bad switch box which would require me to take it into the shop (which I want to avoid).

    Opinions?? Sorry for the long post, but I feel like you guys who have actually used this motor could help me out. I am going to get the carb cleaned first (should I rebuild it? was rebuilt last year, and not used much), and then move into the electrical system, just want some opinions.
  2. Brett

    Brett > PRO STAFF <

    Unused engines are prone to fuel system problems.
    Old fuel, blocked filters, blocked carb passages.
    That'd be my starting point.

  3. DuckNut

    DuckNut Brandon, FL

    The issue with the throttle sounds like the cable is not moving smoothly. When you push the lever forward it may be binding and then it instantly breaks free. Disconnect from both ends and see how hard it moves- it should move with very little pressure.

    Try that first and then report back.

    The knocking may not be the engine but the gears. If your throttle is not working right it may not be allowing it to fully engage.
  4. HaMm3r

    HaMm3r Well-Known Member

    I like Duck's suggestion. That could very well be it.

    However, I've had similar symptoms with a Merc 25 2-stroke and it turned out to be gunk partially clogging the jet in the carb. It was too big to blow through and apparently it would move around and cause the motor to bog down intermittently.

    You might also want to inspect your fuel lines and primer bulb. Make sure there are no air leaks or restrictions. Gas tank vent too.

    Now, why would you need to take the motor in to a shop for a stator, trigger or control box? Those are easy, easy, easy! I can swap a stator on that motor in 30 minutes. That said, the problems you're describing don't really sound electrical. I'd be looking elsewhere first.