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  • #132367

    Tom Jerome
    Participant
    Vessel Name: The Kraken
    Engines: Twin 99' 4BTA 250hp
    Location: chesapeake, va
    Country: usa

    Is there any adjust to the in gear idle speed? Mmy idle in both port and starboard in neutral is about 625rpm. When the starboard eengine is placed in gear it drops to about 545rpns and the port drops to about 580. The port engine runs ok at this rpm but the starboard has a bit too much vibration load and i need to bump it up to match the 580rpm.. these are 1999 cummins 4bta 250hp diamond series. Outfitted on a 99 pursuit express 3000. Thanks for any input

Viewing 6 replies - 1 through 6 (of 6 total)
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  • #133697

    Francis Valerio
    Participant
    Vessel Name: overslept
    Engines: Twin 4BT CPL741
    Location: Massapequa Park, New York Long Island
    Country: USA

    4BT “series” engines are known to shake at idle or just dont like certain low RPMs.  Your 4BTA does have the Bosch P-pump which is an excellent improvement over the CAV pumps on the 150hp version.

    I dont know exactly how the 4BTA handles the RPMs but I would think you need to be a bit higher to get rid of the roughness.

    I know with CAV pumps they need to be higher RPM than what you are at.  I would try 600 possibly to see if that helps.  You are not going to hurt anything at that RPM

    2 users thanked author for this post.
    #133646

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    Adjust the idle to where it feels best overall as the shift, gear rattle, general feel of the boat–The number does not matter

    1 user thanked author for this post.
    #133611

    Tom Jerome
    Participant
    Vessel Name: The Kraken
    Engines: Twin 99' 4BTA 250hp
    Location: chesapeake, va
    Country: usa

    mounts

    the engine mounts on the port are brand new and the starboard are original still in decent shape but set to be replaced this coming winter. Specs for cummins says idle should be 650 +/- 25rpms. I could bump the idle up a tad higher round 675

    #133491

    Tom Jerome
    Participant
    Vessel Name: The Kraken
    Engines: Twin 99' 4BTA 250hp
    Location: chesapeake, va
    Country: usa

    Thanks

    I got a reliable laser and set everything correctly now. Idle is 650roms laser and in gear from dead stop drops to 550rpms but then comes up once we are moving. I have a strong feeling based on some other performance numbers i am over propped. We shall see today though. I just got everythi g calibrated correctly. 

    #133229

    Mark Tripi
    Participant
    Vessel Name: Keeper
    Engines: Cummins 4BTA
    Location: Long Island NY
    Country: USA

    I have the same boat/engines. And had the same problems. Are those idle numbers from the boat tachs or did you use a laser tach? The boat tachs can be off. I would raise your idle up to 700 or so and that will help a lot with vibrations. Are you running with the original engine mounts? They are most likely shot if so and replacing them will also help. 

    #133021

    Tony Athens
    Moderator
    Vessel Name: Local Banks
    Engines: QSB 6.7 550 HP
    Location: Oxnard, CA
    Country: USA

    4BTA Idle screw

    You have a Bosch  p7100 series injection pump.   

    You have a mechanical adjustable idle screw.

    Plenty of pics on the web site to show how it works.

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