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  1. #1

    14 310r still down on rpms... Any ideas?

    I've been through everything i can think of. It's down on rpms and i don't know why.
    Last year it won the first 3 rounds of Aqua x and ran about 7800- 8000 rpms.
    The last moto of round 3 it suddenly lost about 800 rpms and power.
    We found the exhaust filter came loose & plugged the exhaust. After replacing it with a new one the rpms were still low. I believe the blocked exhaust may have caused the motor to get hot. I went through everything i could but found nothing questionable so i tried finishing the season with it. It cost me the championship. After the drop in rpms it was having major oil blowby through the ic and intake. It was spotless until the low rpm issue.
    This off season i did a leak down test. It was over 30% . Compression was 120. So i pulled the motor and rebuilt the topend. New pistons, cylinder, rings and valve seals. Valves were adjusted to spec and checked for leaks. New belt & tensioner
    I just tested it and it STILL is down on rpms.
    I put in a new I/C & bovs.
    Fuel pressure is 55 psi.
    It has decent low end and revs to 7700 for a few seconds then backs down to 7200.
    I just replaced the ecu to the 2015 ecu. It got a little better but only revs to 7700 & still backs down to 7300. The speedo sensor is shimmed with an extra spacer so the speed limiter doesn't effect testing. It will be back to original position for racing.
    KDS has no fault codes.
    Ive even took apart the S/C to check for anything. I greased the end bearings and changed the sc oil. The boost guage seems to read only about 12-13, not 17.
    Could there be an issue with the exhaust muffler or fuel tank check valve?
    Has anyone seen an issue with different types of oil?
    the ski is completely stock with stock prop.
    Anyone have any other ideas? Im out of answers and time.....
    Last edited by H20mxracer223; 04-19-2015 at 08:47 PM.

  2. #2
    Take the time to smile sirbreaksalot's Avatar
    Join Date
    Jun 2007
    Rockwall , Texas
    put a true scom in it to verify the washers arent going you a false reading

    as its obvious that the ECU is getting signal to say reduce the throttle

    and to my knowledge the SPEED sensor is the only input that could do that with out a code


  3. #3
    DH300's Avatar
    Join Date
    May 2013
    The fact that it WILL reach near normal rpm and then back down probably means some ECU issue. If it was a mechanical failure(boost leak, exh. Filter, etc.) it seems like it would never get to 7700 to start with.

  4. #4
    GZA's Avatar
    Join Date
    Sep 2010
    New Zealand
    The simplest thing you should do is remove the (stupid) washers, carry a GPS then go ride the thing and see what it does - if it limits itself to 67, there is no problem. With the washers in, you're getting erroneous signals. Pretty sure someone tried them when the 310 first came out and they had issues straight away - different to the 300's. (Not 100% on this though...)

  5. +1 by:

  6. #5
    nicjak's Avatar
    Join Date
    Mar 2008
    Warragul, Downunder
    I also said to measure the fuel flow of which you havent bothered to report on..

  7. +1 by:


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