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  1. #1

    MSX 140 Cuts In / Out - What to Consider Other than TPS?

    I purchased two MSX 140's last week from local charity. One designated as parts, the other supposedly "checked out" by Polaris mechanic last fall. I am asking about the "good ski" and will have a separate post on the other with different issues. It appears the ski had set for 2 years, was started last fall, had service bulletin stickers and 167 hours. I have done the following:
    Drained gas and replaced. Checked compression (was 105 / 106 consistent with weak battery and I failed to have full open throttle/ yes need to check again), started ski - started fine and would not idle, charged battery and replaced plugs with correct plugs. Ski idles fine (and tells you that either the mechanic was not Polaris or ski was not checked). Checked fuel pressure running none; Clamped hose - 35+ fuel pressure; installed inline fuel regulator. Also, lubed & other general check. Will probably not change hull bearings until summer end.

    I took it to the lake this am for a checkout. Ran fine on trailer. Ran find on first mile - moderate rpm and speed. Stopped and checked hull for leaks & other. Next run Started cutting out or rev limiting. Appears to be happening at around 4400 upon acceleration. But not always the case. Bring it back down to idle and then it runs fine until you get it back up. May run fine at 32 or so. Brought it back up from stop and with constant acceleration ran up to 54 (not GPS) and ran perfect for couple of miles. Drop off and then cutting in / out. Ran for about 10 miles total. No warning lights. Cylinders warm/hot to touch but can keep your hands on. (will check screens and thermostat); Injectors cold to touch. Overall ran excellent except ....

    I assume it is the TPS. Should I just replace and given it another run? Anything else. I have read all posts and this would appear to be course to take but appreciate any advice. I do have the MSX service manual.

    Thanks for all the info you guys have provided over the years. Maybe I can contribute some day.

    Experience - I have replaced an engine (SBT)for sister in XL 1200; replaced piston/fuel pump/rebuilt carbs in SL 750 -which this will replace for wife & which was purchased with a good GP1200.


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    Does the parts engine have a TPS you could swap in for a test? Exact same results means TPS is not the culprit, or not the only problem.

  3. #3
    Parts does have TPS (is complete ski) but I only had limited time on lake this am and will not be able to put back into water until next Saturday/Sunday. And I am not sure of "condition" as both have been sitting and it has other problems. I was therefore thinking of replacing. I actually hope to have "parts" ski in the water next week also as I think it is repairable (another post). I thought I may just start with a good TPS. It was not old style so it may have been replaced.

  4. #4
    I changed the TPS. Ski ran fine for a while but then starting cutting out/ limiting rev at about 32 mph and sometimes when starting. No lights (other than warning and temp flashed once after cut out). Thermostat housing clean. Air sensor cut under air intake. Should I assume this is the problem or just order air and water temperature sensor? I assume I need to pull exhaust for water temp sensor and easy to replace. I do have another ski purchased at same time that was to be a parts ski but it is running great after inline fuel regulator and piston replacement.
    Last edited by WEJ999; 04-16-2013 at 09:50 AM.

  5. #5
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by WEJ999 View Post
    I changed to TPS. Ski ran fine for a while but then starting cutting out/ limiting rev at about 32 mph and sometimes when starting. No lights (other than warning and temp flashed once after cut out). Thermostat housing clean. Air sensor cut under air intake. Should I assume this is the problem or just order air and water temperature sensor? I assume I need to pull exhaust for water temp sensor and easy to replace. I do have another ski purchased at same time that was to be a parts ski but it is running great after inline fuel regulator and piston replacement.
    Check/confirm the EMM actually has decent cooling water flow. The water circuit first goes through the cover of the flywheel housing, then through the EMM, then exits at the rear of the hull, via the exhaust fitting.

    If the EMM is not getting water flow, it will overheat and fail. If it gets well cooked it can damage the electronics, requiring repair. EMM overheat can happen without any warning light or message.

    Polaris revised the air temp sensor mounting with a spacer. You can get the spacer, or just trim back the plastic cover web so it clears the sensor.

    Exhaust temp sensor; Remove and inspect the exhaust water injection orifice, and the mesh filter screen. This is the short water hose that loops across the top of the exhaust pipe. Do not enlarge the orifice, just make sure it is clear and clean.

    Did you check for exhaust leaks? If the exhaust has overheated the rubber hoses may have failed. Stage one is often the internal rubber layer delaminates and partially blocks the exhaust flow, reducing engine power and causing weird symptoms. And/or the exhaust hose or resonator can burn through and leak exhaust into the engine compartment, where the engine sucks it in and cannot breathe properly. If you ride with the seat off and the problem goes away (since there is ample fresh air to the engine), that suggests there is an exhaust leak.

    You can manually check engine temperature with your hand. You should be able to touch any part of the engine or exhaust without burning yourself. If you cannot hold your hand on it for a few seconds, it is probably too hot.
    Last edited by K447; 04-16-2013 at 05:18 PM. Reason: Wrong exhaust sensor info, oops :(

  6. #6
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    The temp sensor is not an on/off switch in the DI motors, it feeds an actual temperature reading back to the EMM. What year are your MSX's? The 2003s had a service bulletin to add a bumper where the exhaust temp sensor mounts to the manifold. The problem is the plastic exhaust tube pinches the wire on the sensor. This was the problem on mine when I bought it. Check that out.

  7. #7
    Click avatar for tech links/info, donation request K447's Avatar
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    Quote Originally Posted by BryanP View Post
    The temp sensor is not an on/off switch in the DI motors...
    Thanks for catching that! Me gets confused sometimes, apparently.

  8. #8
    Quote Originally Posted by BryanP View Post
    The temp sensor is not an on/off switch in the DI motors, it feeds an actual temperature reading back to the EMM. What year are your MSX's? The 2003s had a service bulletin to add a bumper where the exhaust temp sensor mounts to the manifold. The problem is the plastic exhaust tube pinches the wire on the sensor. This was the problem on mine when I bought it. Check that out.
    They are both 2003's. I did not notice the spacer on the "parts" ski that now runs fine. I have not removed the exhaust on the ski that is skipping. I did order a air temp sensor to replace cut sensor as well as check the water lines to the EMM - all clear. The ski had 4 recall stickers but I am not sure which items. Water temp sensor will be next check. Thanks to all. Will let you know. I realize I need to build code checker.

  9. #9
    I replaced the cut air temp sensor. I also checked thermostat, EMM cooling and other cooling - all fine. I plugged and unplugged other connections just to check. I ran for about an hour today - running several intervals. It runs fine. I must assume that the air sensor was the cause of the cutting in and out after running 15 minutes or so. The other MSX that I purchased also had not had the spacer inserted or the fin cut on the air intake to prevent cutting of the sensor. I have "fixed" this one also. Thanks for the input.

    All together on this ski that supposedly had been checked by the charity before sale, I added inline fuel regulator (no pressure), cut rope from shaft and replaced temperature sensor. (I also replaced TPS while searching for problem.) Not too bad all in all.

  10. #10
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    No, not bad at all. Pretty cheap fixes.

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