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  1. #1
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    Your thoughts on my jetting

    Harry.
    Your 1390 motor is a great platform. I have had it a year and it ALWAYS preformed great.
    But I have done some things to it and would like your thoughts on where my jetting should be now.This is what I have and what I am getting.

    I have:
    2002 1200 motor now 1390 group k motor.
    hull has 120 hrs on it
    tunnel renforce
    OLD style r&d ride plate modded by me to for top end.
    new wear ring SS
    plugs indexed and j gapped
    D plate.
    Jet works mod with 3/8 hose
    concord 14/20 pitched to 14.5/24
    2002 pump
    148 psi head presure ( @ 400-500 rpms cranking)
    VF-3 reeds
    3* keyway
    # 3 cylinder dumping water over.
    pilot 95 mains 120
    1 turn out on lows
    1.5 turns out on highs # 1&2 cly #3 at 1 7/8 (plug looked lean.)
    No choke plates or rods,
    pump is sealed and shoe is not hanging.
    1200 R&D intake
    2002 tabs (metal) shimmed .034 front two bolts .054 rear bolts
    pro-tec FA's
    Hull sanded.

    I have not filled any holes in shoe or ride plate or tabs. I am not sure I am where I want to be yet.


    Here is the storie:

    lately I thought maybe the impeller I pitched might have been out of wack? 75.5 mph @ 7210 rpms
    So a freind lent me a impeller that he had done by a pro. it is a 14/20
    pitched up to 14.5/21. I tried it this morning. ran 7310 rpms @ 75.3 mph

    From a motor stand point where do you think the jetting should be? accel. pump still hooked up. Any thoughts?
    Last edited by great lakes gpr 1200; 05-11-2007 at 08:59 PM. Reason: for got data


  2. #2
    Moderator OsideBill's Avatar
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    What needle and seat are you running and what spring?

    IMO you are way low on the jetting what does your pistonwash look like? have you done any plug chops at wot and 1/4 1/2 throttle?

    Most people I know are running 110p 125m on 1200R's with 1.5 N&S and 95 gram spring with choke plates removed 150 heads and d-plate. I know Spud is running 115p and 135m and 2.0 N&S on his ported 1300 seems like the 1390 would need something more in this range.

  3. #3
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    1.5 N&S and 95 spring

  4. #4
    Moderator OsideBill's Avatar
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    N&S and spring are fine might even consider upping to 2.0 but not until after you increase the pilots and mains first and then make a decision on the N&S

    I would also highly recommend you remove the accelerator pump

    how do your plugs look?

    how many hours you have on this set-up?

  5. #5
    I have to agree that your jetting seems very small for this set-up. I'm running 115/130 with a 2.3 ns on my ported 1200.

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