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  1. #1

    MSX 140 centre cylinder, apparent lean failure?

    Hi all , new to this site and looks like some good info. Had many cars and boats but just got my 1st ski. Am auto mechanic / engineer by trade.

    I bought a 2003 polaris msx140 ho here in western Australia not running with pto cylinder water induced.

    Just done full top to bottom rebuild and fired up great.

    Whilst checking the oil output to each cylinder at cranking speeds I thought it was a bit low after bleeding it so decided to add some premix for 1st start up around 15L .
    All was well on about a 1hr ride with low then mid throttle with occasional short wot . Run great and brought it home , used about 7L.
    Took it back out 3 days later added 30L 98 octane unleaded and all was good cruising around. On wot attempt for around 10 sec motor just cut to a lock. Fired back up 5 min later and ran ok then did something on wot again.

    Took home and tested . Comp 130 psi on pto and mag but zero centre. Stripped and had had burn on top of piston towards exhaust side with a hole and complete cylinder score grab.
    Looks definitely like a lean out not lubrication problem.

    Would run fine for ages on max half throttle but will lock on wot any longer than 10 sec only on middle cylinder.
    Checked fuel pressure on water while cruising and a couple stabs and maintained a steady 20 psi.

    Maybe crook injector and or ecu? Not sure if fuel reg mod has been done.
    Any advice would be appreciated.
    Last edited by K447; 01-19-2021 at 10:18 AM.

  2. #2
    Click avatar for tech links/info K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada

    Adding oil to the fuel tank on a Ficht fuel injected engine does not provide any additional lubrication to the engine. The fuel is injected directly into the combustion chamber, where it is instantly ignited and burned.

    More info here

    Has this engine been rebuilt recently, or perhaps the center cylinder/piston was replaced? Wondering if the piston was incorrectly sized.

    Lean burn on these engines tends to create a crater hole in the center of the piston, not the exhaust port area.

  3. #3
    Hi K447 ,
    Yes I just recently rebuilt it . New bearing rods pistons , re nikasil bores etc. Used spi pistons and clearances were perfect. Bores were diamond honed then plateu finished.
    As said pto and mag are still perfect just centre cylinder problem. Yes I agree being Di not fuel and air case reed induction your comment makes perfect sense regarding premix.
    Burn started from centre and got gradually worse towards exhaust side of piston.

  4. #4
    Moderator HiPeRcO's Avatar
    Join Date
    Jul 2007
    Upstate NY

    Can you post pictures of the damaged cylinder?

  5. #5
    Hi mate, not the cylinder but I will try send one of the piston.

  6. #6

  7. #7

    Msx140 leanout

    Hi all , so checked the tank and regulator is intact
    and pressure was 20 psi when tested.
    I'm wanting to get the injectors and ecu tested.
    Where's best place?

  8. #8
    Click avatar for tech links/info K447's Avatar
    Join Date
    Jul 2007
    near Toronto, Canada

  9. #9
    Thanks K , will do.

  10. #10
    Join Date
    Dec 2008
    Hi mate, give ma a call 0421 326 742, I am in Sydney. I can help out with reading EMM and injectors.

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