MerCruiser 5.7L (5.7) Runs Rough at Idle

Question

My MerCruiser 5.7-liter 350 V8 engine runs rough. My MerCruiser motor is a GM .5.7 L competition 4 barrel. What would cause the motor to operate irregular or run poorly while disconnected from a heavy load or out of gear?

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Alonso Daniel 3 weeks 2021-02-13T22:51:00+00:00 0 Answers 21 views 1

Answers ( 3 )

  1. Matthew Moore
    1
    2021-02-13T22:58:25+00:00
    Reply

    You mentioned that the MerCruiser is running poorly and that it idles rough, but you didn’t give me specifics. A rough idle can have different causes as compare to an engine that runs poorly.

    What are the exact symptoms? Knowing what the exact symptom is can make finding a solution much easier. Here are a list of things you should check on your MerCruiser 5.7 L engine under different conditions.

    Carburetor malfunctions

    Engine runs poorly at idle

    Rough Idle

    Idle RPM too low
    Idle mixture screws need adjustment
    Idle passages dirty
    Throttle valve not closing
    Engine flooding
    Vacuum leak
    Throttle body heat passages are blocked

    Engine Surges

    Main metering jets
    Leaking gaskets
    Float adjustment
    Saturated float
    Power piston or valve
    Throttle valves

    Lack of power or lot top speed

    Leaking gaskets
    Main metering jets
    Float adjustment
    Power piston or valve

    Poor cold engine operating

    Engine flooding
    Automatic choke
    Idle RPM too low
    Idle mixture screws
    Throttle valves

    Engine stalls

    Idle RPM too low
    Accelerator pump
    Leaking gaskets
    Automatic choke
    Dirt in carburetor
    Engine flooding
    Idle mixture screws

    Best answer
  2. Matthew Moore
    0
    2021-02-13T23:16:39+00:00
    Reply

    Carburetor malfunctions

    If there is hesitation or acceleration flatness check the carburetor for malfunctions.

    Engine acceleration is poor

    These are more general procedures for troubleshooting acceleration problems.

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