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  1. #1
    jgustman's Avatar
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    Unexplainable new top speed/rpms...

    Something very strange and good happened tonight and I don't quite know what to make of it. Hang on to your shorts for this:
    I have just figured out what looks to be the perfect setup for my 2001gpr 1200. I will not go into detail now, but I hit 74.1 the other night and knew it was a bad run as I was dealing with boat wakes before I topped out. The ski was turning 7240 rpms on the first cold run and missed the top speed. I turned around and returned and hit 74.1 and the rpms had dropped off to around 7190-7200 I believe, wasn't looking closely in superman position. The temp was around 72 degrees I believe.

    Now tonight, I went out at 58 degrees a bit less humid, and never changed the jetting, knowing it was ok from before down to at least 55 deg. Same calm water on the same lake. The ski with the same fuel level (I added about a 1/2 gal back to it) pulled 7320 rpm on the first run at 75.4 and I was watching the gps the whole time and was consistant over 75. I slowed and turned around and did a second run back, water a slight bit rougher and lost around 50 rpm or so, but saw 74.6, feeling I could have go a bit more if I'd stayed in it.

    This same jetting setup has only produced a max of 7240 in the same temps as tonight. I loaded the ski back up and went home not believing what has just occured. The only thing I changed from the last time at the lake was decreasing the shim in the front of the intake grate from .020" to .010". I'm dumbfounded at the rpm increase for no apparent reason. I don't want to go out and now say hey everybody I now have a 1200gpr that runs 75.4 without making some more runs to see if it holds true, I can say 74.6 on the return run should run should be more accurate. Has this sudden jump in rpms ever happend to anyone else???


  2. #2

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    I beleive the weather may have played a big role in your increased rpms.

  3. #3
    jgustman's Avatar
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    I know, I looked at that too, but the only thing I've changed since the last runs at those temps was to pull the front bucket out, I already had the right side cowl opened up this summer. 80 rpm from pulling the bucket???

  4. #4
    Me Hahn and Joe H204YOU's Avatar
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    You had a "Good air day"!I allways check the local humidity so I know what to expect.When the air is cool and humidity is low your numbers will go up.I have been tuning my wifes hull in and have been picking up 3 to 5 tenths each test.I feel lucky tonight also.Her 2000 Gpr has milled head & advent no other engine work,not even jetted(Tamper caps intact).Elev.1260-45% humidity 85 degree heat and hit 72.0 my 2nd time out(heat soak).I am still chippin away,I know theres more there,and a "good air day" will only help I'm savin the superman for later
    Last edited by H204YOU; 10-04-2006 at 09:51 PM. Reason: Superreason

  5. #5
    jgustman's Avatar
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    I don't know what the conditions were at the moment it happened, but I'd guess about 60% humidity at 58 deg. Below are the current conditions 2hr. 45 min. after the run was made.

    Current conditions
    Temperature: 46F
    Feels like: 43F
    Humidity: 71%
    Dew Point: 37F
    Wind: 6 mph NE
    UV Index: 0Low
    Visibility: 10.0 mi
    Pressure: 30.41 in and steady
    Sunrise: 7:26 AM
    Sunset: 6:56 PM

  6. #6
    Duke's Avatar
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    Your temp dropped almost 20 degrees and you picked up 80 rpm. Is that
    what you are saying? Or did I misread?

  7. #7
    jgustman's Avatar
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    You misread, the temp on the first night was around 70-72, the temp tonight was 58. The rpms on this ski have always been consistent around 7240 on the first cold run and 7180-7190 warmed up at temps from 55 to 75 deg. Tonight was a whole different story, gaining 80 rpm over my previous best cold rpms at the same temp...

  8. #8
    spud's Avatar
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    Good Job!!! The air is a big factor. Also the reduced drag on the hull will let the engine spin better.

    You had a "Perfect Run"

  9. #9
    Me Hahn and Joe H204YOU's Avatar
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    Looks like your humidity dropped real fast this evening,not uncommon.The water temps are dropping fast too especially in your neck of the woods,that acounts for your minimal heat soak loss.Those ARE some great numbers,keep up the good work

  10. #10
    jgustman's Avatar
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    Oh great. Now I have to go out and figure out exactly how I postioned my body and monitor the RAD to get a "perfect run" Wait, things are going so well maybe I will try Spraying my nuts with nitrous and hang 10# ankle weights on my feet in superman postion Should be enough to get the entire hull out of the water and hit 90 Hope I don't fall off, I'll sink like the mob put me in cement shoes.
    Actually humidity is going up here as the sun sets and temps drop...
    Last edited by jgustman; 10-04-2006 at 10:13 PM.

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