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  1. #1

    300x - Lower RPM troubleshooting

    Hi guys. I made a post about a week ago where my 300x was hitting 17lbsi boost and then dropped down to 15lbs with a very choppy reading on aftermarket autometer boost guage.

    Mods are as follows. 5 hours on ski total
    R&D scom
    exhaust filter out
    Riva Waterbox
    Riva Freeflow
    Block off
    R&D plate

    This right here may be the inherit cause.........

    I never reset the max rpm on dash. It reads 7310 at 66 mph. Im assuming the 66 mph was before I put on the R&D plate on at 1 hour. But the max rpm like i said is 7310 even the first hour of breakin when ski was stock.
    I checked everything over and noticed that my sparkplugs were all kinda loose. Antiseize was applied on them by dealer and if it wasnt for them being several inches down in the head you could have defintely untightened them with your fingers. I found the correct tourque specs at 9.7 ft pounds and I am assuming that the low max rpm numbers and the slight decrease in boost would be consistent with compression escaping out of sparkplugs if plugs are slighlty loose.
    What doesnt make any sense is why I was originally getting 17lbs of boost for first 4 hours of operation with a max rpm of 7310. Does the ski lock on the max rpm and only reset it when you pull battery and or reset it on dash? Is the rpm even accurate on these since I know the old GP and Gpr platforms you needed a tiny tac for accuracy.

    I will reapply antiseize and take her out tom and see if the plugs were the issue. What do you guys think about the max rpm and the plugs? I need to get gps numbers too.

    PS. The first 4 hours of operation with me and my fiance riding, the ski beat a rxp, stock 300, and a 21 ft checkmate with 200hp. I am very happy with the performance of this ski when she is running full potential.


  2. #2
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    What's your question exactly. ? Yes the max rpm is not a good indicator. Read the actual rpm and look at it while running

  3. #3
    Should the plugs be torqued down differently if using antisieze? Are the factory dash rpms accurate? I will report back sunday late afternoon with an update on actual rpm readings.

  4. #4
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    Quote Originally Posted by mjkzeus View Post
    Should the plugs be torqued down differently if using antisieze? Are the factory dash rpms accurate? I will report back sunday late afternoon with an update on actual rpm readings.
    If you don't know how tight to do them then use a Tq wrench but it's fairly simple. Install the plugs crush the washer loosen retighten hand tight then 3/4 turn

  5. #5
    I torqued them down to 10 ftlbs. See what happens tom afternoon.

  6. #6
    Self Confessed Day Dreamer toomanytoys's Avatar
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    The max RPM is the RPM when the ski hits its maximum (limited) speed not the maximum RPM achieved in general. If you read the digital RPM you should see 7900-8100 at full speed.

    Why the boost pressure drops from 17 to 15 is a mystery to me. If you said you didn't have the SCOM I'd say that's normal. Get a GPS and make sure you are running above the limited speed. You should see 72+ mph.

  7. #7
    nicjak's Avatar
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    max rpm reading on the dash has been explained many times its not max rpm at max speed, when the speedo wheel maxis out it records the rpms but this can be miss leading due to the wheel skipping on the water.
    a good way to test and see what i mean is, reset the dash to zero, start the ski on the trailer have it idling, the max function will not be recording anything, now spin the speedo will with your finger and you will get a max reading

  8. #8
    Hey there my friend......

    Do you have the boost guage mounted in the glove box?

    Feel free to email me [email protected]

  9. #9
    nicjak's Avatar
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    isnt this the ski you had problems with at zero hours? you made such a big fuss back then why arent you taking it back to the dealer with your problems? why take the exhaust filter out? its been proven time and time again there are no gains with it removed just the opposite actually good luck with that!!

  10. #10
    Quote Originally Posted by nicjak View Post
    isnt this the ski you had problems with at zero hours? you made such a big fuss back then why arent you taking it back to the dealer with your problems? why take the exhaust filter out? its been proven time and time again there are no gains with it removed just the opposite actually good luck with that!!
    Yes it is the ski i had problems with at 0 hours. I dont feel like wasting more of my summer taking off the few minor boltons and driving an hour to the dealer and waiting even more time. Big fuss?? Whos making a big fuss? Trouble shooting the cause and effects on here.

    Anyhow, I pulled all spark plugs and re applied ant iseize and tourque them down to 10 ft lbs. Ski ran terrific and my rpms were perfect at a max of 7730 and thats with the solas 14/21 prop in. Boost guage still reads 15 lbs but is not sputtering all over the place like before. From what you guys have told me I am assuming at those current rpms #'s that my boost reading of 15lbs is good. Still cant figure out why the first 4 hours I was getting 17lbs of boost, but again my rpms look good and shes running like a beast. I guess I was leaking a bit of compression out of 1 of the spark plugs.

    I will reinstall the exhaust filter tonight. as per all your guys recommendations.

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