Logo
Results 1 to 9 of 9
  1. #1

    Default Mercruiser 350 not running right

    A few months back we bought a 2003 20i Tige ski boat.

    Took it for a test run before buying and it ran great for the 30 minute test run.

    In the months since buying it Iíve had some upholstery work done, I put on FAE stainless mufflers, and I fixed a few other cosmetic items.

    Last Saturday everything was finally back together, so Sunday it was lake day! Boat started up great, idled out of the ďno wake zoneĒ great, and I hit the throttle to get going fast. Fifteen seconds later the motor throttled down by itself and started ďcoughingĒ. I pull the throttle back and the engine coughs then dies. I check around under the engine cover and everything seems fine. Start it back up and itís idling great. At this point my daughter is on the tube floating behind the boat and wants to get pulled around. I pull her in idle foe about a minute and everything looks/seems/sounds great, so I throttle up. Itís running perfect for about 10-15 seconds then it chokes and throttles down by itself, and ultimately dies.

    This happened over and over, so we yanked the tube and just went for about an hour idling cruise, ate lunch and headed home.

    Iíve worked on engines quite a bit when I was younger, and the only things that came to mind was bad gas, in-line fuel filter, or fuel/water separator. So yesterday I changed filter, separator, and I put an addictive in the fuel. Hooked up to water in the yard this morning to test out. Idle was fine, but at 2500 rpms it lasted 15-20 seconds. Next I took the air filter off. Now I got 2500 rpms for a full minute! Thinking I need to get a new air filter, I was just about to throttle down and shut off. Well, the motor beat me to the throttle down, same issue.

    All local boat mechanics are 3-4 weeks out, and I have a house boating trip planned in 2-1/2 weeks!

    What is the next thing that I check?

    Your help would be very much appreciated

  2. #2
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    8,866

    Default Re: Mercruiser 350 not running right

    what did the fuel in the old filter look like?

    When was the boat last run, before you bought it?

    engine make and fuel delivery system type?

    Boat engines don't have air filters - they should have flame arresters and they usually need cleaning when the oil and filter get changed...

    if it is fuel injected, I'd do a fuel pressure test...

  3. #3

    Default Re: Mercruiser 350 not running right

    Quote Originally Posted by makomark View Post
    what did the fuel in the old filter look like?

    When was the boat last run, before you bought it?

    engine make and fuel delivery system type?

    Boat engines don't have air filters - they should have flame arresters and they usually need cleaning when the oil and filter get changed...

    if it is fuel injected, I'd do a fuel pressure test...
    The fuel in the old filter looked fine, no signs of water.

    I bought and test ran the boat back in March. Prior to that the boat apparently hadnít been started since last summer.

    Fuel injected Mercruiser 350


    With the flame arrestor off, boat still runs bad after 30 seconds of higher rpms.

    I havenít done a fuel pressure test, and honestly thatís something Iíve never done on a boatÖÖ. I am awaiting a call back from a mobile mechanic, and that is something that he can do. In the meantime, I will research online how to do it myself.

    Thank you for the reply.

  4. #4
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    8,866

    Default Re: Mercruiser 350 not running right

    could also be the anti-syphon valve...especially if the fuel wasn't stabilized before storage...

  5. #5

    Default Re: Mercruiser 350 not running right

    Quote Originally Posted by makomark View Post
    could also be the anti-syphon valve...especially if the fuel wasn't stabilized before storage...
    anti-siphon valve located on fuel tank?

  6. #6

    Default Re: Mercruiser 350 not running right

    Quote Originally Posted by makomark View Post
    could also be the anti-syphon valve...especially if the fuel wasn't stabilized before storage...

    Top of tank

  7. #7
    Join Date
    Sep 2008
    Location
    Maryland - USA
    Posts
    8,866

    Default Re: Mercruiser 350 not running right

    yes, on top of the tank, usually the first fitting out of the pickup tube...it will look similar to a hose barb fitting...google it for some examples...

  8. #8

    Default Re: Mercruiser 350 not running right

    Problem has been solved…. It was a bad low pressure lift fuel pump.

  9. #9

    Default Re: Mercruiser 350 not running right

    Problem solved.

    From the fuel tank to the motor, the fuel follows this path.

    Tank, anti-siphon valve, in-line filter, low pressure lift fuel pump, fuel/water separator, fuel cooling system, high pressure fuel pump…….

    Problem was a bad low pressure lift fuel pump. The high pressure pump was able to suck enough fuel through the whole system at low idle, but at higher RPM’s it just couldn’t supply enough without the help of the lift pump.

Similar Threads

  1. Mercruiser 260 running hot maybe.....
    By Bdaniel808 in forum Mercruiser Sterndrive Forum
    Replies: 0
    Last Post: 08-15-2018, 10:29 PM
  2. 140 Mercruiser dies after running a while.
    By Bob Komischke in forum Mercruiser Sterndrive Forum
    Replies: 5
    Last Post: 07-09-2011, 03:34 PM
  3. Mercruiser 470 running hot
    By zparrish103 in forum Mercruiser Sterndrive Archive
    Replies: 6
    Last Post: 05-23-2009, 06:50 AM
  4. Mercruiser 43 running hot
    By sharkin95 in forum Mercruiser Sterndrive Archive
    Replies: 4
    Last Post: 10-18-2008, 09:10 PM
  5. Mercruiser 260 Running Hot
    By Jerry Barth in forum Mercruiser Sterndrive Archive
    Replies: 3
    Last Post: 08-04-2008, 12:57 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •