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  1. #1

    Default Help! Mercury 100

    I recently acquired a non running Mercury 100hp 2t. Within a few hours I got it to crank up and run. 125psi on top 3 cylinders 119 on bottom number 4. Timing is all dead on, can hit the key and it'll fire right up and idle. I deleted the oil tank and pump so I could 50:1 premix.

    My problem is. I cannot get any throttle response out of this engine. Within the first 10 minutes of idle it's loading up. Won't shut off but man o man the smoke. Raise the rpm to clear it up some engine levels off and cleans up. Drop it in gear throttle up some and it's like it just goes into limp mode. It's a junk yard motor. Multiple engines to make 1. No serial numbers that I know of, from what I can tell it's a complete engine with safety stuff and alarms. Just zero ass when it comes to running. Almost like it's lost its 2 stroke "power band" and sound. Sounds nothing like a high strung 2 stroke when revving. Almost instant rpm drop after throttle decrease. It doesn't have that ping ping ping like a chainsaw.

  2. #2

    Default Re: Help! Mercury 100

    Excess Smoke indicates high oil that is partially burnt %. Have you checked the idle and total timing while running in water against resistance? Going limp may be a symptom of stroke hapenning at incorrect times just sufficient to run the motor but not have the power to run it while against resistance while in water.

  3. #3
    Join Date
    Sep 2010
    Posts
    17,424

    Default Re: Help! Mercury 100

    Check fuel pump diaphragm.

  4. #4

    Default Re: Help! Mercury 100

    Quote Originally Posted by AMT View Post
    Excess Smoke indicates high oil that is partially burnt %. Have you checked the idle and total timing while running in water against resistance? Going limp may be a symptom of stroke hapenning at incorrect times just sufficient to run the motor but not have the power to run it while against resistance while in water.
    I have not had a chance to check timing while on the water. Been doing everything by myself. So far everything's been done in a drum with the exception of a few circles on the lake with disappointing results. I premix my oil 50:1. I've cleaned the carbs multiple times. Set idle mixture screws on top 2 carbs. Set floats. Cleaned accelerator pump jets and checked them for leak by. If I starve it for fuel or 20:1 mix nothing changes still smokes like a chimney at idle. Around 1k rpm it'll clear up on a 50:1 mix but has no twang. I've raced dirtbikes for years 2 stroke being my engine of choice. When i first fired this motor up it sounded like a cracked out dirtbike. It sounded like a beautiful orchestra of 2 stroke power. Now it's just blah.

  5. #5
    Join Date
    Sep 2003
    Location
    New Tripoli, PA, USA!
    Posts
    16,214

    Default Re: Help! Mercury 100

    50:1 is leaner than 20:1 (which is richer), but that's not the issue here.

    Try this: Run the fuel line around (by-pass) the fuel pump and see how she runs. Have an assistant GENTLY pump the bulb to keep gas in the carbs. If she clears up, change the fuel pump diaphragm (which would be a good idea in any case).

    Jeff

    PS: Lacking expansion chambers, OB 2 strokes don't really have the 'sound' we all loved back in the day. (I raced MX/ hill climb, and endures for years!)

  6. #6

    Default Re: Help! Mercury 100

    I'll try bypassing it here in a hour or so. I'll post a video of it running as it sits and let you know if that helps or not

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