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  1. #1

    Default Pcm 351 - engine bogs down under load

    1991 sunsport

    runs great out of water.....but in water bogs down when try to get on plane.......anyone had this problem.

    Holley 4160 - rebuilt
    gas tank drained cleaned
    fuel pump cleaned.

    The boat has been in storage for 7 years, so i cleaned everything and took it for a spin. 1st trip went great...ran strong but at the end of the day started to bog down on occasion.

    2nd trip.....again ran fine....drove across lake and sat for awhile....then when started back up......bogged down on way back to ramp.

    Driveway tests - runs strong----steady at 3000 rpm and strong bursts to 6000-6500 rpm.....runs great

    3rd trip - week later

    engine fires right up.....taxi thru no wake zone.......give it some throttle and nothing.......bogged down....

    Any help would be greatly appreciated....

    Shawn

  2. #2
    Join Date
    Jul 2007
    Location
    Flowery Branch Georgia
    Posts
    2,551

    Default

    What ignition do you have points or electronic? Check the distributor advance weights make sure they are free.

  3. #3
    Join Date
    Apr 2002
    Location
    Florence, AL
    Posts
    777

    Default

    I would check the fuel tank vent for obstructions and replace the fuel filter. In that order. Sticking distributor timing advance weights mentioned by Michael is also something to check on.

    Don't spin that motor to 6500 or even 6k in neutral. The valve springs aren't strong enough and you can get valve float, and possibly smack a valve into a piston at those speeds. I'd call 5k-5500 absolute MAX, but there's no reason to spin it anywhere near that fast.

    My first guess based on the all of your symptoms is a clogged fuel filter.
    1992 Supra Mariah - Red
    PCM 351HO 285hp - PCM 1.23:1 Transmission
    OJ XMP 4 Blade CNC 13x15.5RH

    "People do weird things to boats" -Unknown

  4. #4
    Join Date
    Jul 2010
    Location
    N.W. Suburbs Chicago, IL
    Posts
    2,253

    Default

    This boat also falls into the range of Pro-Tec ignition as well. If it has it that could also be an issue.
    '86 Comp TS6M - Reborn 2016
    Riding a HO Sports CX Ski

  5. #5

    Default

    Yes, It does have the ProTec ignition.....I am checking the fuel lines....the ball check valve this weekend.

    Filter was already replaced....will check again.

    Thanks

  6. #6
    Join Date
    Apr 2002
    Location
    Florence, AL
    Posts
    777

    Default

    Quote Originally Posted by Jetlink View Post
    This boat also falls into the range of Pro-Tec ignition as well. If it has it that could also be an issue.
    Agree 100%. Hated my ProTec. Boat never really ran right and finally it started limiting to 2k RPMs in limp home mode. Best and only mods/repairs done on my boat were replacing the pro tec with the SKIDIM Mallory distributor retrofit kit and replacing the Holley 4010 carb with a 80319 model Holley 4160. It purrs like a kitten now. Aside from rough idle at initial start when cold, you'd be hard pressed to tell the boat isn't EFI.
    1992 Supra Mariah - Red
    PCM 351HO 285hp - PCM 1.23:1 Transmission
    OJ XMP 4 Blade CNC 13x15.5RH

    "People do weird things to boats" -Unknown

  7. #7
    Join Date
    Jul 2010
    Location
    N.W. Suburbs Chicago, IL
    Posts
    2,253

    Default

    Quote Originally Posted by 1991smg20259 View Post
    Yes, It does have the ProTec ignition.
    I bet we have found your problem right here.
    '86 Comp TS6M - Reborn 2016
    Riding a HO Sports CX Ski

  8. #8
    Join Date
    Jul 2007
    Location
    Flowery Branch Georgia
    Posts
    2,551

    Default

    Davis Unified Ignition distributor is your friend.

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