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  1. #1
    ecpChris's Avatar
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    Weird SHO problem

    I've been having a weird problem with my ski since I've owned it. I can't go full throttle and hit max rpms for more than a few seconds. Once the ski planes out and starts hitting max rpms the rpms suddenly drop. When I was running a prop that was too big I was maxing at about 8050 rpms. Within seconds it would drop to about 7880. Now that I just recently bumped up from r2 to r3 and pitched the prop for 8500 the rpms peak around 8550 then it feels like if hits a limiter and drops to 8150. It's the weirdest feeling and I can't figure out why it's doing it.
    Mods are intake, exhaust, powercooler, ET low boost, 13/22 skat.
    Any ideas what would cause it? Now that the rpms are up the problem seems exponentially worse... Almost like someone hits the brakes at max rpms
    Thanks


  2. #2
    Antiguan FZR's Avatar
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    Sounds like it may be lean, have you tried an AFR?

  3. #3
    ecpChris's Avatar
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    Quote Originally Posted by Antiguan FZR View Post
    Sounds like it may be lean, have you tried an AFR?
    Not yet I'm waiting on the o2 adapter. It was doing it with a riva b1 wheel at only 8k rpms so I didn't really think it was that. Changing to the ET wheel and r3 just made it worse

  4. #4
    THE PLATE MAN JIM'S PERFORMANCE's Avatar
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    If you are in the limiter hard it will do that mine would go from 8700 to 8100 and once you ease up on the throttle it would shot the rpm's up again.

  5. #5

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    based on your mods you have way to low of pitch prop for your ski a 14/24 should be a better choice. I supect you are hiting the revlimiter just as Jim suggested. Tommy Jordan

  6. #6
    SurfRider's Avatar
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    The problem is that when it was 13/24, he would not see over 8100 rpm and then it would drop to 7800.

  7. #7
    SurfRider's Avatar
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    The only other thing I can think of that would nail it that fast would be the knock sensor. It would retard the timing and slow down the ski. You do have Premium fuel in there right?

  8. #8

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    Quote Originally Posted by SurfRider View Post
    The problem is that when it was 13/24, he would not see over 8100 rpm and then it would drop to 7800.
    wow then it's not a prop /rpm issue. I here of a ski that had a similar problem the rpm's would run up for a few seconds then fall back a few hundred. The problem was that this motor had excessive ring blow by (30% + ring leakage) and after a few seconds the crankcase pressure built up excessive causing the rpm drop. Just a thought. Tommy Jordan

  9. #9
    gordon lasiter #328's Avatar
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    Quote Originally Posted by SurfRider View Post
    The only other thing I can think of that would nail it that fast would be the knock sensor. It would retard the timing and slow down the ski. You do have Premium fuel in there right?
    are you running 91 octane of good quality fuel?
    with he r2 or r3 reflash you should be running 93 or 95 octane. as long as you use chevron 91 you should be ok.
    when i was reading your post the first thing that popped in my head was "FUEL PRESSURE" do u have a rrfpr?
    if you do i had good luck with 52lbs @ static with a c3 wheel.
    i was also running with a 14/23 skat and with a 85mm ring i would be at 8400 to 8500 rpms with zero rpm problems.

  10. #10
    ecpChris's Avatar
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    Filled up with 93 and added a shot of toluene just in case. Wasn't rev limiter problem either ad it was hot out and max rpm on my tach was 8545. It is so weird it shoots up to max rpms really quickly then dies to 8100ish and starts creeping up again but at that point I just let off.
    It kinda did the same thing when I had the r2 and b1 setup but it would hit about 8050 then drop down to 7880. Any other thoughts?

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