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  1. #1

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    1999 Gp1200 Carby Rebuild / Tune Check List

    Hi Everyone'

    Firstly thank you very much for all the information i've been able to gather so far, the forums have been great!

    Im going to be rebuilding my carby's in the coming weeks for the First time so wanted to make sure I had everything covered.

    It is a 1999 Yamaha GP1200x (non p.v)

    History of the ski, only had it out 5 times myself, has 170hrs, as per previous owner said he rebuilt it himself as his a boat mechanic 20hrs ago (comp readings though are 112,114,112 which seem low for fresh rebuild) Oversized Pistons, New Piston Rings, Port & Polished, New Crank , Pro-Tec Intake Grate and Solas Impeller, Running Pre-Mix 50:1 Yamalube.

    Reason for rebuild of carby's firstly on a few days out it would bog down a bit under 4000rpm and according to the tacho on full throttle would'nt rev past 6200rpm after backing off a bit would rev to 6400rpm. Last time I took it out it started making a loud popping noise from the what sounded like the exhaust manifold area when i was just puttering along and ended up cutting out and wouldnt start, took it out of the water and it started but still wouldnt rev out. I pulled the exhaust manifold off and the #1 and #3 exhaust ports were quite fueled up and Oily which leads me to think could be needle and seat issue from what i've read. Checked all vacumm lines and compression which was all ok and I cant see any other issues so narrowed it down to the carbys which could possibly untounched since new for all I know (Now 170hrs).

    Carby Rebuild Kits ill be using:
    http://www.ebay.com.au/itm/MIKUNI-SU...item2eb7d5bfaa

    I will use the 115g Spring

    Needle & Seat 1.5
    http://www.ebay.com.au/itm/MIKUNI-SB...item2eb815c58e

    Removal of Choke Plates & Adding Primer Kit
    http://www.ebay.com.au/itm/MIKUNI-TR...item43a4d7bb33

    As suggested on the forums ill also be removing the Choke plates to get more air into the carby's and adding a fuel primer kit.

    High & Low Settings
    Low: #1: 1 Turn #2: 1 Turn #3: 1 Turn
    High:#1: 3/4 Turn #2: 1 Turn #3: 3/4 Turn

    Because ill be removing the Choke Plates should I Up the high settings abit further than above ?

    Also out of the water it idles around 2000rpm and in the water it idles at 1100rpm, does this sound right in the water or should I turn it up a notch ?

    Any help/suggestions/feedback more than appreciated!!!!!

    Thanks In Advance Everyone and sorry for the lengthy post!
    Last edited by brady89; 10-25-2011 at 09:53 PM.


  2. #2
    DAGO RACING CREW 97GPSLEEPER's Avatar
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    I had a needle and seat stick on me along time ago and it filled #2 cylinder with fuel and read like 50psi of compression, ran like shit and would barely get on plane. All that fuel in the cylinder is what gave it the low compression reading, nothing else was wrong. Another thing to consider on your slightly low compression readings is that you state the cylinders have been ported. Having bigger ports is going to lower your compression. Also, I did not read anywhere in your set up that you have a milled stock head or aftermarket head. Stock compression is 120-125 with the throttle held open and a fully charged battery. Being your ported and have done nothing to raise your compression, your compression readings are fine in my opinion.

    I would bring the idle up between 1200-1300 rpm. Also, I would open up the low speed settings half a turn to start with after adding a primer. When you richen your low speed settings your are also slightly richening your high speed circuit as well. However, adjusting the high speeds mixture does not have any effect on the low speed mixture. To be safe richen the high speed mixture 1/4 of a turn after the primer install. Do you have an aftermarket tach? This is a critical tool in getting it tuned right and insuring you don't have seize while getting it dialed in.

  3. #3
    Yamaha artisan Cutlass's Avatar
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    If its ported, you may have to rejet the carbs a bit. Take some pics of the porting and post them here. Also post up what size jets you find in the carbs when you open them up.

  4. #4

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    Thanks for all the info and tips there 97GPSLEEPER & CUTLASS !!

    I started pulling the #3 carby apart and taken pics at each step aswell for later reference when putting them back together.

    Sorry but this is very newbie of me (first time ever working a jetski and pulling a carby apart) but where abouts is the jet in the carby and how will i know what size it is ? ( I Presume its just inside where the fuel lines go into the carby) ?.

    Also this is what i found the screw settings to be at on each of the carby's.
    (Im not sure if I did this right but i measured it by how many full turns (360deg) to the right till it was all the way in)
    #1 H: 1 3/4......L: 1 1/8
    #2 H: 2............L: 1 1/4
    #3 H: 2............L: 1 1/4

    To me this seems way off to what the high and low speed screws should have been set at and maybe why it has bad holeshot and not much topend ?

  5. #5
    Yamaha artisan Cutlass's Avatar
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    The jets are on the side with the needle and seat and are under the kidney bean shape "valve body". The jet size is stamped on the jets.
    Just for reference, my screw adjusters are set at: H: 1 1/2 and L: 1 1/4 turns out.
    Its better to be a bit rich, then lean. Also, unless you have a well established combo of parts/engine mods, you jets and screw settings are gonna be up to you to figure out and turn. Some of us can give you a good place to start and you'll have to tune from there.

  6. #6

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    ok i took the jets out but from what i could read it didnt say like 100, 120, 135 etc etc.. im at work now but from memory it had like R3 or something. Is there a part code on them that refers to the size jet it is?

    Also I've taken out the Reeds/Cages and one of the reed petals has a gap of about 5mm from the frame and the petal next to it is also slightly torn.. I take it I should definatley be replaceing these? Should I go aftermarket or just stock replacement?

  7. #7
    Yamaha artisan Cutlass's Avatar
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    I like the OEM stock reeds myself. They are very durable.
    The main jets have the number stamped in the top near the screw driver slot like this (I think it says 172.5):


    And the pilot jets have the numbers on the side like this (It says 102.5):

  8. #8

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    thanks heaps for the pics!! ill check as soon as I get home.

    I have K&N Flame arrestors and an R & D Ride plate coming in the mail now. From what I read if I dont mill the head then I should be fine with the standard jetting.
    Mods: Oversized Pistons, Port & Polish, Pro-Tec Intake Grate, Solas Impeller.
    K&N Flame Arrestors + R & D Ride Plate - Soon to be installed.

  9. #9
    Yamaha artisan Cutlass's Avatar
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    Porting will require rejetting and the K&N flame arrestors will require you to change the pop off pressure.
    How much porting are you doing? Are you porting the case and the cylinders?

  10. #10

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    All mods were done by previous owner: Oversized Pistons, New Piston Rings, Port & Polished, New Crank , Pro-Tec Intake Grate and Solas Impeller.
    Im just waiting on the R & D Ride Plate and K&N Flame Arrestors which I will be putting on myself.

    Compression is at 112psi accross the cylinders.

    I am waiting on parts for the carby's and will be using 1.5 Needle & Seat and 115g Spring...

    After doing some more reading it is suggested to drop the pop-off pressure when using flame arrestors.. so should I use the 95g spring instead ?

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