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  1. #1

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    MSX 140 Runs Rough at low-mid RPM range

    After reparing my thru-hull bearing carrier the vibrations I had at idle are now completely gone and it idles real smooth.

    However the rough running issue occurs mainly when the engine is cold, i.e. when it is first accelerated. The engine appears to bog down, vibrate a lot, but when given more gas it picks up and goes after a few seconds. The machine can hit 60 mph on the speed-o (not GPS) and RPM gauge appears to top out at 6900. If it is on smooth enough water it will bounce off the RPM limiter, drop about 200 RPMs, then go back up to the limiter again.

    Once the engine has seen some high RPMs it no longer bogs down at low RPMs (I assume since it has warmed up), however the motor still generates a lot of vibration (particularly around 2-3k RPMs)

    Is vibration normal in that RPM range? What do you think could cause the initial rough running and bogging at low rpms? My initial thought is the exhaust temp sensor.... However it could also be the TPS eventhough I replaced it a year ago, Perhaps ill try putting the old TPS back in to see what it does.


  2. #2
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    The Polaris 1200s all run rough in that 2500 ish range

  3. #3

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    Quote Originally Posted by BryanP View Post
    The Polaris 1200s all run rough in that 2500 ish range
    Okay thanks.

    I still don't understand why when the machine is first started, and say, your idling away from the dock (first run of a given day) it bogs and hesitates for a couple seconds before taking off when you give it more gas. Then after you have revved it up a bit, it no longer hesitates from idle until the engine is allowed to cool down again.

    It doesn't seem normal to me, but I feel like it has done it consistently over the 3 or 4 years that I have owned the ski. Any thoughts on that? Or is that just how the ski normally operates?

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    My guess is that the engine is still quite cool when you first try to accelerate. Even a Ficht engine can stumble sometimes when not yet warmed up.

    I typically start the engine on land and let it run for 10-15 seconds, burp the throttle to confirm it is responsive, then shut it down. Back it down the ramp, then idle again once it is launched. After maybe 30-60 seconds of idling. I will start adding some power, but avoid wide open for another couple of minutes.
    Last edited by K447; 08-04-2014 at 06:54 PM.

  5. #5

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    Thanks for the replies guys. Yeah generally once I give it a little throttle and get it past about 3k RPMs it clears up. I'll just take it a little bit easy when initially launching.

    It is just hard to do so because once I get about 30 or 40 feet away from the dock I can just take off since there is no speed limit

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