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Engine idles erraticly after a hard run; often refuses to be started.

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  • Engine idles erraticly after a hard run; often refuses to be started.

    Background:
    2005, 210 hp “Carb Jet Drive” [a 2-stroke outboard on a Mercury SportJet pump], engine model S210J10DD, Engine serial# OE427816.

    I change the plugs and the fuel filter at the start of every season (currently at this end of the season, hardly 20 hours of running), and I use only highest AKI grade of gasoline (in this area, 91) at a busy, Top-tier gas station (it's a trailer boat); also treat the fuel all year appropriately (Sta-Bil 360 Marine, and BioBor EB). The injector oil I use is AmsOil fully synthetic.

    Now the Problem:

    Toward the end of this season, my otherwise good running engine started idling erratically after a nice run (3 to 3.5K rpm) around the lake. It wouldn't return to a reliable idle rpm as I slowed for the buoy line, and it often stalled.

    When it did stall, I couldn't crank it in the usual fashion: after it cranks for barely a second, the starter would stop as if the battery was dead (at first, it fooled me enough to replace the battery), but it really wasn't bad as I discovered later -- because if I pulled the neutral release on my Morse shifter and opened the throttle (either reverse or forward), then the engine cranked nicely. So it only refused to crank when the throttle was in the normal neutral (throttle at idle) position.

    Even so, after cranking the engine and starting it up, it would still idle poorly or stall again. This is only a problem after a long, hard run -- when I start off at the beginning of the day, it seems to run fine.

    This is a relatively new problem. Earlier in the season it ran perfectly, as well as in many earlier years.
    1) Why has the idle become erratic after a long run?
    2) Why is it difficult to crank the engine, seeming like a dead battery, if the throttle is in (slow) neutral?
    I suspect that these are related???

    Any and all suggestions will be appreciated.

  • #2
    1 - either crud in the fuel or your motor is running hot
    2 - most likely your motor is running hot

    check the motor temps with an IR gun
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari

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    • #3
      Rebuild the manual fuel pump and check carbs. Could have one flooding.
      When in doubt,Trim it out!!!
      Business Owner & Certifed Technician
      Boats I own & use
      20ft Javlin w/250 Junkrude
      17ft Bullet w/200 Merc (SOLD!!)
      13ft Allison w/150 I-6
      17ft Hydra-Sport 175GT
      15ft Allison w/75 Stinger(project)
      14 x 48 Drifter with 1100SS Merc

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      • #4
        Sounds likes it’s flooding to me too when hot, do as stated above and also check the engine temp valve that comes from the starboard cylinder head, it is open when motor is cold to allow more fuel into motor to help start when cold and should be closed when hot so it doesn’t flood motor. It has a hose connected to it and a second barb with nothing on it. I believe between the bottom two spark plugs.

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        • #5
          No thats backwards leon.....the thermal air valve is closed when cold in order to restrict air to the idle circuit so that there is a richer fuel mixture when the engine is cold. When the engine warms up, the valve should open to allow air to the carb circuit during idle.
          When in doubt,Trim it out!!!
          Business Owner & Certifed Technician
          Boats I own & use
          20ft Javlin w/250 Junkrude
          17ft Bullet w/200 Merc (SOLD!!)
          13ft Allison w/150 I-6
          17ft Hydra-Sport 175GT
          15ft Allison w/75 Stinger(project)
          14 x 48 Drifter with 1100SS Merc

          Comment


          • #6
            Sign up today
            Woops, your right got it messed up but it still needs to be checked and is a cheap fix.

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