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  1. #1
    butterbean_29512's Avatar
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    gp1200r carb mod results

    Hello all....just did the carb mods and drilled return mod and water tested today. Set the screws to what OSB recommended in the sticky. My WOT speed is 60, rpms are about 6800. Thought that was low, swapped out impeller and checked, about 7000-7100 with the worn out one. 60 is gps speed, I'm about 215. Plugs look great, runs great, only thing is it loads up after a long idle. I'm running socks. Does anybody have to adjust from the recipe? Are my numbers satisfactory so far? I'm thinking I could close the lows 1/4 turn or go up to 115 gr. springs. What say the GPR experts?


  2. #2
    Quote Originally Posted by butterbean_29512 View Post
    Hello all....just did the carb mods and drilled return mod and water tested today. Set the screws to what OSB recommended in the sticky. My WOT speed is 60, rpms are about 6800. Thought that was low, swapped out impeller and checked, about 7000-7100 with the worn out one. 60 is gps speed, I'm about 215. Plugs look great, runs great, only thing is it loads up after a long idle. I'm running socks. Does anybody have to adjust from the recipe? Are my numbers satisfactory so far? I'm thinking I could close the lows 1/4 turn or go up to 115 gr. springs. What say the GPR experts?

    Don't change the springs. VERY common to tweak the adjusters.

    If you did T handles, adjust the lows 1st, since it also has a small effect on the high speed circuit.

    Lift out the battery box, release the zip ties that prevent getting the box well out of the way,

    Reach under the carbs and work your way forward adjusting the lows.

    I've done GPR's that leaning out the low picked up noticeable top speed, since the recipe setting is errs on the side of rich.

    Lot's of small variables that differ ski to ski. If you have a tach, you can then work the high's.

  3. #3
    butterbean_29512's Avatar
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    I am overall very happy with the way it runs now. It doesn't have the gigantic increase in power I was expecting, but it runs well. And, the plugs have a great color! It is a tad rich though. If I can get the loading up to a minimum, I'll be satisfied with it. I did install new adjusters, so it will be fairly easy. I have to trim a fuel line at the mag carb, so I will just jerk the pipe out. I am thinking maybe 1/4 turn will get it. Also, what RPM is everyone getting from this model ski? This is my first GPR, and the first one I have worked on, so I have no baseline. Also, compression numbers are 112, 112, 110

  4. #4
    ~7k-7.2k That is where it makes peak horsepower(7k), but remember, most forum members mod there skis.

    The recipe affects throttle response and the lean mid-range, mainly.

    Did you cut the hole in the pipe support plate, so you can get to the High adjuster hidden underneath?

    When you get the adjusters tweaked, the recipe should make a noticeable difference off the line, and really pull strong to peak speed which should wind up ~62.

    Your welcome.

  5. #5
    butterbean_29512's Avatar
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    Did not think about cutting a hole for the high adjuster underneath, but my accel pump is still there, so it'll be a pain even if there's a hole in the bracket. If a modded boat is around 7, then my unmodded one is about right at 6800, and I haven't had my glasses on to be able to read the tach, so I'll try and wear them one time to check. And if 62 is max for stock.....I'm knocking on the door, so I'm close! BTW I appreciate the help....I'll post my results after more tuning Monday.

  6. #6
    63.5mph @7100 is a general figure for a new stock ski. That's for ~120psi compression. Lot's of factors that fit into the general wear category, scrub speed.

    Make sure the ride plate is smooth.

    The hole cut has no effect on the accel pump. Have you seen where to cut the hole? If you've got a door knob hole saw it's a good size ~2-1/4 if I recall.

  7. #7
    Huntersthmsn74's Avatar
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    Im at 60 GPS on a 2000 GPR with 120hrs with a FULL tank of gas and glass water. I am at 100psi comp all around. And with these skis all i have heard that it is way better to be rich, than lean....

  8. #8
    butterbean_29512's Avatar
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    I'm at the same spot with mine. Did the carb recipe, and mine is way rich at idle, will load up if idled for more than 15-20 seconds. I have my screws set at the recipe suggestion, and I'm gonna tweak the lows tomorrow, see if I can get it to stop loading up. Other than that, it starts and runs well. I'm well pleased. I will return and report tomorrow with tweaking results. BTW, what are your WOT rpms, if I may ask?

  9. #9
    Huntersthmsn74's Avatar
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    On the small tach i bought it shows between 7100 and 7200 at WOT, I have seen higher but im guessing that is when i hit some chop and the pump unloads and cavitates. Its kinda hard to read when going that fast and its refresh rate is like every second. I have the stock impeller on right now, but am going to switch it out for a solas 13/19 this winter when its not as damn hot outside.

  10. #10

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    Did you set the pop off to 42-45 psi?

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