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  1. #1

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    03 MSX 140 missing and max 5,100 rpm

    03 MSX 140 HO 2 stroke that is missing and tops out at ~ 5,100 rpm. The other identical ski get ~6,500. I pulled the sparkplugs. The middle cylinder was fouled (wet/black). The other two were dry/brown. I ordered 3 sparkplugs and only got one delivered. Changed the new plug with the foulded plug and cleaned the other plugs. It didn't help. I bought two skis this year with 9 hours. I have 35 hours now. Worked good until few hours ago. I am using 93 octane gas (no ethanol) and synthetic 2 stroke oil. Called repair shops around within 50 miles. If they even sound like they would work on it they are backed up a month. Any Ideas? thanks


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Welcome

    Have you checked compression?

    What spark plug are you using?
    Should be NGK PZFR6H - no substitutes.

    Click here for the service manual.

    Click here for other useful info

    A well running MSX 140 in stock form will turn around 6800-6900RPM, give or take.

    I would suggest checking the basics, just to know what is what;
    Compression, fuel pressure, injector voltage, correct spark plugs, ignition coils ohms, plug wire ohms, ignition coil ground to engine block, etc.

    Let us know what you find (if anything), and we can go from there.

  3. #3

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    What spark plug are you using?
    Should be NGK PZFR6H - no substitutes
    .

    Hey K447 do you ever sleep? You are a great resource to everyone. Do you get paid by the post? ;->
    Yup. The replacement plug is PZFR6H. They are projecting to deliver the other two tomorrow. I will have to buy some tools to check the others things you mentioned. I was in a auto shop today and asked for a fuel gage that fit a schrader valve and they couldn't come up with one. This is a small town. I have a compression tester. Didn't want to get that deep yet.

  4. #4

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    Now all the spark plugs are new and OEM. Didn't help. It misses pretty good around 2400 to 4400 then it evens out around 5,000 rpm wich is top end. Don't know if it is still missing just so fast of rpms that I can't tell if it is missing.
    Bought a furel pressure gage and rigged up a flushing system for the cooling to I could do it in the driveway. The fuel press runs around 24 psi at idle. I squeezed off the return line to the tank and the pressure went up to 46. Then back to 24 psi when released.
    I am about ready to get my compression test out and do that but thought I would post this.
    What a way to spend a 4th. Working on the ski.

  5. #5

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    When I pulled the plugs for the compression test, the middle plug that has about 3 hours on it had a really white isulator where the other two that had been in there for one hour were dark. See attachment. Does this mean the injector is bad?
    I did the compression test without the throttles open (oops). I got 118 to 117 on each cylinder so it is consistant. I didn't realize what I did until I had everything back together. I ohmed a bunch of sparkplug wires, coil Primary & secondary. Those seemed to be OK. I noticed my air temp sensor had been smashed by the air cover support. I omhed it and it was at 1 where it should be 990-1000. I will replace it. I looked at the same sensor on the other ski that is running. It didn't look as bad but was a 1 also. That ski runs good, so how important is the air temp sensor? see attchment.
    Making a slow go of it.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  6. #6
    Click avatar for tech links/info, donation request K447's Avatar
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    Compression test on the fuel injected engiens is not affected much by throttle open or closed. More important on the carbe'ed engines.

    Temp sensor - did your meter switch to K-ohms, and show you 1 K-ohm reading.
    1 K-ohm =1,000 ohms

    That center spark plug looks like it has not seen any combustion.

    Either no fuel injection or no spark in that cylinder.

    Is there any sign of sparking on the tip or the ground electrode?

    Mark all three injector bodies (not the metal brackets) with which cylinder they are on. Then swap the front and center injectors. Do not over torque the injector bolts.

    Don't run the engine really hard with swapped injectors, but run it enough that you can see whether the center spark plug shows signs of combustion.

    If swapping injectors doesn't help, then the EMM may need repair.
    Last edited by K447; 07-07-2009 at 07:14 PM.

  7. #7
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    From my experience, it will take some time for the new plug to change color.
    It would be better to switch the plug if you are going to switch the injector.

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by casey67 View Post
    From my experience, it will take some time for the new plug to change color.
    It would be better to switch the plug if you are going to switch the injector.
    I was trying to figure out if the center cylinder was getting spark but not fuel, or fuel but not spark.

    How does moving the clean spark plug help the diagnostic?

  9. #9

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    Quote:
    Don't run the engine really hard with swapped injectors, but run it enough that you can see whether the center spark plug shows signs of combustion.

    Reply:
    I took one injector from my other identical jet ski. I ran it for about 30 seconds (with cooling water). It sounded rough but when I pulled the plug there was black smudges from combustion. So it is my injector, right? Can they be repaired? I thought I read that if an injector is replaced it had to be hooked up to the computer and "tuned" in or can I do it?

  10. #10
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by craig4him View Post
    Don't run the engine really hard with swapped injectors, but run it enough that you can see whether the center spark plug shows signs of combustion.
    ...I took one injector from my other identical jet ski. I ran it for about 30 seconds (with cooling water).

    It sounded rough but when I pulled the plug there was black smudges from combustion. So it is my injector, right? Can they be repaired?

    I thought I read that if an injector is replaced it had to be hooked up to the computer and "tuned" in or can I do it?
    I was thinking more like riding it for 10 minutes or so with the injectors changed at under 1/2 throttle

    You have two identical MSX 140?
    Well, that opens up a bunch of diagnostic possibilities!

    It is possible for the injector to be bad, but I have not heard of many actually failing.

    Most Ficht failures are the EMM itself, the stator or flywheel, and sometimes the ignition (coils, plug wires). This would be after confirming the fuel pressure is good, of course.

    Another common failure possibility is the TPS and/or the TPS connector.

    The fact that it sounded rough doesn't make me comfortable.

    Put the original injectors back as they were. Swap in the EMM from the 'good' engine. You can run the engine continuously for a minute or so without worries, with the cooling water flowing.

    If you can, it is much better to diagnose with the jet pump in the water, where the engine will have a load to work against.

    See if it still sounds rough with the 'good' EMM installed.

    Also wiggle the TPS connector while the engine is running. Any change of engine speed indicates a poor connection, which needs to be fixed.

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