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BF 75 (75 HP) No power above 2500 RPM

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  • BF 75 (75 HP) No power above 2500 RPM

    Trying to help out a friend with a carb'd 4-stk 75hp Honda, probably '97~'99 model. The engine runs fine, although a little rougher at idle than I would expect, up to approx. 2500 RPM under a load. If you open the throttle from that point, the engine looses all power until you back off the throttle. It seems to be loosing cylinders, but will return to below 2000 rpm smooth as silk. We've even attempted to pump the fuel bubble when the problem occurs to make sure the fuel pumps are maintaining the carb bowls, no success. One thing that leads me to electronics is that if you maintain the throttle open for an extended length of time, the engine will flood, this kinda leads me to believe that the fuel delivery and air is OK.
    We've gone through the simple stuff; good gas, clean carbs, plugs, oil pressure and temp switches, and the electronics ohm out normal by the service manual specs. There's not much information on how the electronics function in the Honda Service manuals, but I suspect either a coil or a pulse sensor may be bad.
    Anybody ever run across something like this? Hoping to avoid going through a lot of expensive electronics parts to find the issue. No reliable/helpful Honda dealers in our area to help as well.

    Thanks
    Mike

  • #2
    Run a compression test first to see if all cylinders are even. Use a timing light to see if it's loosing fire to a cylinder.
    Regards
    Boats.net
    Honda Outboard Parts

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    • #3
      Compression

      Yep...did that as well...no issues....should've listed that as well....also, I've got a lot of experience with 2-stk outboards (Merc, OMC, Yam, ect) been building and racing them a long time, just not much reference with the 4-stk's. If this was a Merc or OMC I'd typically say it was a stator issue or another component that's breaking down as the demand goes up at the higher RPM. Does anyone have any DVA type measurements for testing the elecs while the engines are running? That's another usual indicator when electronics are suspect.

      Thanks Again
      Mike

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      • #4
        If timing light didn't show any misfire then could be a timing problem(check with timing light), valve timing(check belt timing is ok) or could be a fuel issue carbs or fuel pump problem.
        Regards
        Boats.net
        Honda Outboard Parts

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