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  1. #1

    Join Date
    Mar 2008
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    Michigan
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    anyone running the groupk 1390 kit?

    I would like ot hear feedback on their 1390 kits. I really like their idea of ditching the powervalves and the fact that their 1390 kit actually turns less rpms, I am looking for a small increase in power but want to increase reliability as much as possible. Their kit seems to address alot of the inherant weaknesses in the 66v engine based on the write up at their site and they seem to have a solid reputation.

    who is running their kits or has experience with their work, service etc?


  2. #2
    SpeedJunky's Avatar
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    Dec 2005
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    Michigan
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    No experience with the 1390 kit but have had GroupK do machine work for me in the past and have only good things to say.

    Another thought would be to talk to Lowell Horning at http://www.2-stroke-porting.com/ he is absolutely the nicest man you will ever deal with.

  3. #3
    dhoad's Avatar
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    Aug 2005
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    North Aurora, Illinois, United States
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    I know "great lakes gpr 1200" is running a group k 1390 with good results, plus he lives in Mich also.
    hopefully he will respond or pm him
    I second the Lowell recommendation. I know he does the motors without PV if thats the way you want it. Or go gas valve.
    I have done 2 motors with Lowell and couldn't be happier with results
    Last edited by dhoad; 03-31-2008 at 03:41 PM. Reason: .

  4. #4
    Bryan K's Avatar
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    Mar 2007
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    Trinity, FL
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    284
    I just got my Lowell 1390 back last Thursday and had Jim's Performance put it together. I have nothing but good things to say about both of them. Everything looke perfect and I have 5 hours on my ski with 0 issues. I have a lot of tuning and some more break in to do and still hit 79.5 mph on gps. I think this ski will run 81-82 with the right set up and be very reliable.

  5. #5
    Mine is the EFI 1390 Low compression 87 octane version from Lowell. Has 40+ hours on the motor. Keeps running better... My signature says it all..

  6. #6
    Moderator OsideBill's Avatar
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    GroupK's set-up is very conservative. Lowell will set yours up any way you want it. I went with the Lowell 1300 and 1390 BB set-ups.

  7. #7
    YudLuz2's Avatar
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    Flowood MS
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    I really doesn't matter which company you go with,
    the deciding factory on reliability issues is the person
    that will be installing and tunning the setup. We all use the same
    pistons, cylinders.... and close to the same compression
    numbers. There's nothing wrong with the Yamaha power
    valve setup. Breaking a valve is not a common issue and if
    it did break or the pin came loose its a slim chance it would
    even drop down to catch a piston. The most common thing I see
    is someone using that excuse for a failure when its the furthest
    thing from the truth. Lower rpms can be as bad as high rpms.
    Your timing curve is much higher at a lower rpm and could
    cause a higher level of deto wich comes with higher temps.
    A single pipe 1390 can rev in the 7500 rpm range without problems,
    and I have ran stock bottom end 1200 motor in the 8000 rpm
    range with triples with great results.
    I have ran Group K, Lowell's and my own with good results. There
    seems to be no known issues with any of the kits. Just proper
    break in , setup, tunning is the key.
    I recommend getting someone to help if your not experience
    in setting up a boat. Good luck with your project.

  8. #8
    sleeplessnMS's Avatar
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    Lower rpms can be as bad as high rpms
    Yep i agree 100% on that!

  9. #9

    Join Date
    Mar 2008
    Location
    Michigan
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    Quote Originally Posted by sleeplessnMS View Post
    Yep i agree 100% on that!

    the kit and porting i want to get will only spin 50 rpms less than a stock gpr with a 14/20 solas prop and with premium pump gas. like i said I am not looking for all out performance just a nice increase in power and a simpler more reliable machine. stock pipe, stock carbs etc etc so conservative is kinda what I am looking for. I am perfectly happy with the top speed it had before it popped, just want to address the low end and mid range and get rid of some of the stock prop and hull's quirks with a ride plate, new prop, ppk, and some other items and give the rebuilt engine more low end/mid range grunt.

    thanks for all the replys guys, keep em coming

  10. #10
    Quote Originally Posted by yamahafreek View Post
    the kit and porting i want to get will only spin 50 rpms less than a stock gpr with a 14/20 solas prop and with premium pump gas. like i said I am not looking for all out performance just a nice increase in power and a simpler more reliable machine. stock pipe, stock carbs etc etc so conservative is kinda what I am looking for. I am perfectly happy with the top speed it had before it popped, just want to address the low end and mid range and get rid of some of the stock prop and hull's quirks with a ride plate, new prop, ppk, and some other items and give the rebuilt engine more low end/mid range grunt.

    thanks for all the replys guys, keep em coming
    I've heard the Group K runs and holds up fine but just know that there is a "dead zone" in the rpm range that the ski will not run in. Not sure exactly where it is, but between say 5000-6000 rpm the engine will just "jump" from one rpm on up and will not run in that particular range because of the lack of powervalves with the porting.

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