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Mikuni Carburetor Test Procedures

The following procedures test the Fuel Pump and various carburetor functions to make sure they are working properly and within specifications. The Pop Off test requires you to use a hand pump Pop Off Tester (Sea Doo #295000114 or similar) with a gauge range from 0-60 psi. Generally, any Pop Off reading under 15 psi is a failing unit and needs repair.

Picture A

Picture A

Fuel Pump Verification
Check fuel pump valves operation as follows:

  1. Connect a clean plastic tubing to the fuel inlet nipple (see Picture A) and alternately apply pressure and vacuum with the mouth. The fuel inlet valve should release with pressure and hold under vacuum.
    CAUTION: Some fuel may be present in fuel pump. Be careful not to swallow fuel when testing.
  2. Repeat the same procedure at the fuel outlet nipple.
    This time the outlet valve should hold with pressure and release under vacuum.

Fuel Pump Diaphragm Leak Test
Using a suitable pump gauge tester (like Sea Doo P/N 295000114), perform the following test as follows:
  1. Install pump gauge tester on the pulse fitting (see Picture A).
  2. Pump the tester until it reaches 28 kPa (4 PSI) on the gauge.

    The pump diaphragm must stand pressure for 10 seconds. If the pressure drops, replace the pump diaphragm.

To Check Mikuni Internal Filter
To verify filter condition proceed as follows:
  1. Remove pump cover, gasket, diaphragm and then pump body and gasket.
  2. Remove filter from carburetor body then clean filter and blow carefully with compressed air (low pressure).
  3. Replace filter if damaged.

    While apart, inspect valves (flaps) and diaphragm. The pumping area should be free of holes, tears or imperfections. Replace if damaged.

Pop Off Pressure Test
Proceed as follows:

  • Install pump gauge tester on carburetor inlet nipple (see Picture A).
  • Obstruct outlet nipple with a finger.
  • Pump tester until inlet release pressure is reached (seen by a sudden pressure drop).

    Refer to the following tables for Pop Off specifications for various models.
    Arm Spring Load (g)
    Valve Seat Dia (mm) 51 65 80 115
    1.2 29 ± 8 38 ± 10 48 ± 12 76 ± 15
    1.5 17 ± 5 27 ± 8 33 ± 10 42 ± 12
    2.0 11 ± 4 16 ± 5 21 ± 7 29 ± 8

    MODELS POP OFF(min.) POP OFF(max)
    1996 SP,SPI,GTS 21 37
    1996 SPX,GTI,HX 40 56
    1996 XP 27 39
    1997 ALL MODELS (EXCEPT SP,XP) 27 39
    1997 SP 21 37
    1997 XP 36 40
    1998 GS,SPX,GTS,GTI 36 40
    1998 XP Ltd, GSX Ltd, GTX Ltd 19 23
    1999 SPX, GS, GTS, GTI 36 40
    1999 XP Ltd, GSX Ltd, GTX Ltd 19 23
    2000 2001 2002 GS, GTS, GTI (& LE) 36 40
    2000 2001 2002 XP, GTX 19 23

    1994-1995 Models - Release pressure (sudden drop) should be 22-29 psi for single carb and 16-21 psi for dual carb models.

    1993 Models - Release pressure (sudden drop) should be 21-32 psi for ALL models.

    If the release pressure is not within specifications, check control lever adjustment and also replace spring as necessary.

    NOTE: Pressure test should be performed three times to obtain a the proper reading.
    CAUTION: Do not stretch or cut spring.

    Leak Test
    Needle valve must stand a pressure of 69 kPa (10 PSI) for 30 seconds.
    If it doesn’t, hold carburetor upside down, pour oil over needle valve and retest.
    Check for bubbles. If they come from seat or O-ring, bubbles will exit around seat. Retighten as necessary.
    If it still leaks remove needle and seat and replace O-ring.
    If bubbles come from needle, replace needle and seat.

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