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  1. #1
    Predator-x's Avatar
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    GPR running little lean

    I have a fresh rebuild 2001 GPR and running lean on the rear cilinder ,used jetting specs by OsideBill.

    1200R Aftermarket F/A's (Flame Arrestors) chokes intact.
    • 110 Pilot jets, 1 turn out on low speed adjusters
    • 120 main jets, 1-1/2 turn out on high speed adjusters
    • 1.5 Needle and Seat, 95 gram spring (Dull Silver) 42-45 avg. pop-off pressure.
    Pop-off pressure came out on 43 with restrictors drilled out and used a 95 inline restrictor jet.
    Pressure tested the engine at 10 PSI and have a loss of 3 PSI in 5 min. ,that would be in the acceptable range.
    Modifications are free-flow exhaust and D-Plate.
    Plug from rear cilinder had a grey/white colour after running.
    What do you guys suggest? , Richen up the the third carb with the high speed adjuster or do i need another jetting specs ?


  2. #2
    mudslanger's Avatar
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    Is that the only mods. have you done anything to the timing. can you post some pics of the plugs.

  3. #3
    Predator-x's Avatar
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    That are the only mods related to the engine , i forgot to mention running premix en disabled accelerator pump.
    I didnīt toch the timing, donīt know if the previous owner did something to it, can it be told from the outside ?
    Plug of the lean cilinder fell on the ground and the porcelain broke so i tossed it away, not a smart move now i think of it.

  4. #4
    mudslanger's Avatar
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    seeing the plug would help. there are a few things that can result in the plug color that you are describing. I have seen timing do it and also water getting it from a small crank in the cylinder. it can be mistaken for a lean condition. but you need to make sure it is not lean. I would fatten that carb at least a 1/2 turn and run it and post some pics of the plugs.

  5. #5
    Predator-x's Avatar
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    I will post pics of the plugs after running ,now itīs still a little cold to go on the water but iīll try to run the ski within two weeks.
    Carbs are currently on the workbench to install the T-handles i bought from Bill a while ago.
    To be continued !

  6. #6
    Predator-x's Avatar
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    Did a new engine pressure test with 6 psi instead of 10 psi ,10 psi seems a little too much what iīve red in some posts.
    Pressure holds for more than 30 min so it looks i have a air tight engine.
    Installed the carbs with T-handles and fatten up the high speed needle for the last cilinder 1/2 turn.
    Only have to drill a hole in the stinger bracket so i can access the last T-handle for adjustment if needed, and wait for the weather to warm up.
    Will update after speed run.

  7. #7
    Predator-x's Avatar
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    Today took the GPR to the lake for testing .
    Fatten up the rear carb 1/2 turn at the HS needle but still a grey color spark plug .
    Fatten up even more the rear carb by 1/2 turn more but still no color change ,and the ski takes of a little slow (i had to play the throttle to rev up).

    Plug pics are from left to right ,rear-mid-front .

    Click image for larger version. 

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    Click image for larger version. 

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  8. #8
    Superman! fivespeedsteed's Avatar
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    I thought it was 1 psi over 10 minutes. I had a motor I just built leak 2.5 pounds in 5 minutes. I got new crank seals flipped motor over split case put new rear seals in, old inner seal had a small nick in the seal. New ones hold way better. Like 1/4 of a psi in 10 minutes. What was leaking when you pressure tested? If its rear crank seals that can be why #3 is lean. Especially if running it has made it leak more

  9. #9
    See what others have to say but I would be almost inclined to pull the head off and check #3. Have you compression checked #3. I would expect lean to be more white.

  10. #10

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    Grey seems a little too much like vaporized aluminum to me. Better pull the head and check out the piston edges.

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