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  1. #1

    98 GSX-L jetting change - requirements

    I just purchased 2 used 98 (1997.5) GSX-L's these are the white motor 951's

    At present the jetting is (below) with stock flame arrestor

    2.0 N/S with 95 gram spring (25psi pop-off)
    162.5 Mains - 0 turns out on high speed screw
    77.5 pilots - 1 1/4 turns out on the low speed screw (low speed screw is good from 1 to 1.5 TO) so a happy in between
    Accel pump lever in contact with plate and working

    Installed an R&D flame arrestor and the boat seems to run good up to 3200 rpm and over 4200 rpm - this is the rpm range when the boat is plowing, just before coming up on plane..

    As you take it up through the rpm's with a slow steady increase in throttle the engine is not smooth between those rpm's - kinda like it's fuel related - ba bap ba bap ba bap and you can see the motor shake..

    Is this rpm the transition stage - a jetting issue or a pop off pressure issue

    I turn 6950 rpm and idle at 1100 rpm in the water.. Water and air temps in mid 70's


  2. #2
    Is this jetting the same as the silver motors? IIRC when BRP rebuilt blown engines, they reset jetting to silver specs.

    Read post 26

  3. #3
    It has been advised to use a 2.0 N/S and a 95 gram spring - But that combo yeilds a 25 psi pop-off..

    (Although 21 psi is usually recommended)

    Which would require a 85 gram black spring with a 2.0 N/S or a 95 gram spring with a 2.3 N/S

    It has been advised to use 82.5 and 85 pilot jets (although the stock silver motor uses a 75 pilot jet) (only the white motor uses a 80 pilot jet)

    (But it is recommended to jet to silver motor specs)

    It has been advised to use 162.5 - 165 - 167.5 and in that post 182.5 (typo??) main jets.. (although 162.5 is pretty much stock on all 951's)

    See there is a big differance between the specs posted and the recommended info given..

    If you spec a 95g spring with a 2.0 N/S - why reccommend a 21 psi pop-off ??

    If you spec a 82.5 LS jet - why reccommend silver motor specs ??

    So I am confused and thus the question..

  4. #4
    Solved.. As Qouted from Bill O'Neil -

    The 1997.5 ('98 ) GSXL with the white engine has some really off the wall parts inside the carbs. The carbs were completely redone in 1998 grey motor models.
    1. The needle valves were increased in size to 2.0
    2. The Gold 115 gr. springs and the spacer under the springs is eliminated and replaced with a dull silver 95 gr spring and no spacer at all.
    3. Both the low and high speed jets sizes are increased to 82.5 LSJ and 162.5 HSJ.
    4. The low speed adjuster goes from 1 3/4 turns out down to 1 1/4 turns out
    5. The piston to cylinder clearances were opened up to .005" to prevent siezures

    The external changes are rotating the two carbs 180 degrees on the intake manifolds so that the diaphrams face rearward and the accellerator pump is moved from the front of the carb set to the rear of the carb set. This is a much more accepted way of running the carbs and Sea Doo has allways run the I series carbs that way since they were first introduced on the '94 XP motors.

    There were some other important changes made to the engines when they went from the cast aluminum prototype 947 white engines to the die cast silver 947 engines. For those reasons, the only thing internally in the engines that interchanges with the two engines is the pistons, rods and crankshafts and counterbalancer shafts..

    There is water jackets inside the upper case halves of the silver motors, the clyinder is slimmer on the white motors so the clyinders cannot interchange because the upper cases are different widths.

    The '97.5 GSXL had an amplifier and a TPS throttle cable that was eliminated in 1998 red deck GSXL's. I'm sure it has to do with the TPS's ability to switch timing curves in the mpem, and I'm pretty sure that Sea Doo programmed the most fuel efficent curves possible to emit less pollution from unburnt fuel in the combustion process.

    Bottomline is the pop off needs to be between 19 and 25 psi. I perfer 19-21 psi with aftermarket filters, thus I use 2.3 x 95 gram springs.

    If the accellerator pump works good, maximum of 85 pilot jets. I increase the high speed jets a minimum of 2.5 points

    947 engines, with nothing but A/M filters at sea level, 85 pilots x 165 mains x 2.3 N&S x 95gr, springs. Pretty much oem adjuster settings.

    OEM silver motors after mid 1998 have 2.0 x 95gr. x 82.5 pilots and 162.5 mains. These specs are with an active accellerator pump with clean diffuser nozzels.

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