Engine slows down

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by speakrdude, Jan 25, 2019.

  1. speakrdude

    speakrdude Active Member

    Feb 21, 2009
    Northwest Arkansas
    2002 Sea Ray 340 DA
    Raymarine C80 Tri Data
    twin 6.2 MX MPI
    so, a quick question for some of you mechanically inclined, with experience with this year/style engine.
    2002-340. 6.2 mx engines.
    Stbd engine was said to be freshly rebuilt when i bought. Both orginal 650 hours.
    Both start idle perfectly. Run super smooth throughout rpm range.
    However, full throttle, after warm up, port engine 5k rpm ish.
    Stbd engine may hit 5k briefy but then gradually slows down to 3500.
    No butps, farts, sneezes, just looses power. Havent changed anything except fuel/water seperator/ oil/ basic maintence.
    This is my first mpi. Have service manual. Where to look first?
  2. Espos4

    Espos4 Active Member

    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    A Fuel pressure test would be tops on my list.

    Set up a gauge and have a helper record the fuel pressure as you drive.
    speakrdude likes this.
  3. CliffA

    CliffA Well-Known Member GOLD Sponsor

    Dec 29, 2009
    Lake Norman, NC
    2001 Sea Ray 340DA
    Name: 'Happy Place'
    4.5kW West. Generator
    Purchased Nov. 2014
    Fresh Water Use
    Twin Merc. 6.2L (MPI)
    640 hp (Total)
    Raw Water Cooled
    V-Drive Transmissions
    next time it happens open the fuel filler cap for the starboard fuel tank...if the problem goes away the vent line for the starboard fuel tank is clogged.....

    northshore and joeyleggz like this.
  4. speakrdude

    speakrdude Active Member

    Feb 21, 2009
    Northwest Arkansas
    2002 Sea Ray 340 DA
    Raymarine C80 Tri Data
    twin 6.2 MX MPI
    Thats a distinct possibility. That tank you must put fuel in slowly or it will burp it back at you.
    The port doesnt have that problem at all.
    northshore likes this.
  5. stg099

    stg099 Active Member

    Jun 30, 2013
    2004 280 Sundancer
    4.3 Mercs/Alpha
    I think you found your problem then... Same thing happened to a guy on my dock, once the vent line was blown clear he was good to go.
  6. TNT8808

    TNT8808 Active Member PLATINUM Sponsor

    May 25, 2016
    West Michigan
    2008 48 Sundancer
    Cummins QSC 8.3's
    Avon Seasport 340
    40 HP Yamaha
    This reminds me of a time we were up in Pentwater a couple of years ago, and a guy and his wife were slipped next to us and had a similar problem with their Regal. All of us dock mechanics narrowed the problem down to his starboard vent line, and he said he could see some type of spider nest in there by leaning overboard and looking in there with a flashlight. We all suggested he disconnect the hose from the inside and blow or suck it out. Next thing we know he's leaning overboard with the central vac in hand. I'm pretty sure you all know what happened from there. He got the nest out all right, and filled his vac with gas. They were still there when we left, and still trying to air that boat out. I believe they rented a place in town to stay while they worked things out.

    Rusted Nut and speakrdude like this.

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