Home. Back. ......Jetting Suggestions
Jetting Specifications, 1993-2002. Updated 2/1/02.
1992 GT25/93 GT25E: THE JETTING IS GOOD FOR MOST APPLICATIONS.
STOCK ALTERNATIVE ABOVE 6000'
MAIN 90 95 90
PILOT 33 36 (38 OK) 38
NEEDLE 2ND CLIP FROM TOP 2ND CLIP FROM TOP TOP CLIP
NEEDLE SIZE D36 D36 D36
NEEDLE JET 268 268 268
SLIDE #40 #40 (cut 1 or 2mm from cutaway) #40
FLOAT HEIGHT 26MM 26MM 26MM
NOTE: Alternative is very good at sea level to 6000'
TO MAKE A '91 GT25 DELTA,A '92 GT25,OR A '93 GT25E (1993 GT25E IS THE ECONOMY MODEL WITHOUT CASE REED MOTOR) RUN AT CHAMPIONSHIP LEVEL OF POWER DO THE FOLLOWING:

THIS WAS TESTED BY RISING SUN IMPORTS FALL 1993.THESE MODIFICATIONS WILL YIELD A DRAMATIC INCREASE IN TOTAL POWER OUTPUT OF THE ENGINE OVER ALL RPM RANGES.

BOYESEN DUAL STAGE REEDS
2 BASE GASKETS (93 ECONOMY MAY HAVE THIS ALREADY)
GT32(327cc)FRT.EXHAUST PIPE (LARGER INSIDE DIAMETER AND LENGTH)
#404 IGNITION MODULE(BLACK BOX) FASTER ADVANCE OF IGNITION

JETTING:

#50 SLIDE (#40 FILE 2mm FROM CUTAWAY)

#38 PILOT JET

#95 MAIN JET

#270 NEEDLE JET (CLIP POS.2ND DOWN)

CUT AIRBOX LID 2CM LARGER OPENING(FOR AIR INTAKE)

1992 GT32: THE BIKES WERE RICH AS DELIVERED. MOST PEOPLE WERE SATISFIED WITH STOCK. WE EXPERIMENTED WITH SOME ALTERNATIVES.
STOCK ALTERNATIVE ABOVE 6000'
MAIN 98 86 (92 OK) 90 (92 OK)
PILOT 33 38 36 (38 OK)
NEEDLE 3RD CLIP FROM TOP TOP OR 2ND TOP CLIP
NEEDLE SIZE D36 D36 D36
NEEDLE JET 268 268 268
SLIDE #40 #40 #40
FLOAT HEIGHT 26MM 26MM 27MM
1993 GT16: THE BIKE MAY RUN RICH IN MID-RANGE WITH STOCK JETTING. THIS IS THE REASON FOR THE CHANGE OF THE SLIDE CUTAWAY. LEAN ON BOTTOM END POWER WITH HESITATION IS THE REASON FOR THE RICHER PILOT JET.
STOCK ALTERNATIVE ABOVE 6000'
MAIN 95 95 86
PILOT 38 42 (40 OK) 42
NEEDLE 2ND CLIP FROM TOP 2ND CLIP FROM TOP TOP CLIP
NEEDLE SIZE D36 D36 D36
NEEDLE JET 268 268 268
SLIDE #30 #40 #40
FLOAT HEIGHT 25MM 25MM 27MM
1993 GT25T: THE STOCK JETTING DELIVERED IS GOOD FOR SOME BIKES, BUT OTHERS ARE RICH AND REQUIRE REJETTING. THE FOLLOWING INFORMATION WAS SUPPLIED BY GASGAS R&D IN SPAIN.
STOCK ALTERNATIVE JIM SNELL'S SETTINGS
MAIN 95 95 95 (92 OK)
PILOT 33 38 38 (36 OK)
NEEDLE 2ND CLIP FROM TOP 2ND CLIP FROM TOP TOP CLIP
NEEDLE SIZE D36 D36 D36
NEEDLE JET 270 270 268
SLIDE #40 #40 (CUT 2MM) #50 SEE BELOW
FLOAT HEIGHT 24MM 27MM 27MM
FUEL SCREW 4 TURNS OUT 4 TURNS OUT
On Jim's settings NOTE: If you wish to run unleaded Premium gasoline rather than race gas use #95, the #92 main may cause spark knock.
TO MODIFY THE 93 GT25T JETTING: (NOTE:GT25T BIKES BUILT AFTER JULY 1993 HAVE THE SLIDE MODIFIED AT THE FACTORY. IF THE #40 STAMPED ON THE INSIDE OF THE SLIDE HAS BEEN DRILLED OUT, THIS IS A FACTORY MODIFIED SLIDE. IF YOU SEE THE #40 STAMPING YOU HAVE THE UNMODIFIED ONE.) CHANGE THE PILOT FROM A #33 TO A #38 OR #36, AND FILE 2mm FROM THE CUTAWAY ON THE AIRBOX SIDE OF THE SLIDE. (OR REPLACE WITH A No.50 SLIDE). BE SURE TO CHAMFER THE EDGES TO PREVENT THE SLIDE FROM STICKING IN THE BARREL OF THE CARBURETOR. SET THE FLOAT HEIGHT TO 27mm (STOCK IS 24mm) TURN THE FUEL SCREW TO 3.5 TO 4 TURNS FROM THE INMOST POSITION. MAKE SURE THAT THE NEEDLE CLIP IS IN THE SECOND SLOT FROM THE TOP. TAKE 2cm FROM THE INSIDE OPENING OF THE AIR BOX LID. (THIS IS TO ALLOW A FREE FLOW OF AIR TO THE CARB)
GT25T USED BY GASGAS UK IN ENGLAND, NOT TESTED BY GASGAS USA:

MAIN: 95
PILOT: 35
NEEDLE: 2ND OR 3RD
NEEDLE SIZE: D31
NEEDLE JET: 268
SLIDE: 40
FLOAT HEIGHT: 25mm
FUEL SCREW: 3.25 TURNS

GT25T ABOVE 6,000 FT.ELEV:(TESTED AT 1993 UTE CUP) 8,500 TO 11,300 FT.IN COLORADO ROCKIES

MAIN: 90
PILOT: 38
NEEDLE: TOP CLIP
NEEDLE SIZE: D36
NEEDLE JET: 270 (268 OK)
SLIDE: 50
FLOAT HEIGHT: 26mm(27mm OK)
FUEL SCREW: 4 OR 5 TURNS OUT

1993 GT32:AS PER GASGAS RACING DEPT.
SUGGESTED ALTERNATIVE
MAIN 98 95
PILOT 33 42
NEEDLE 2ND CLIP FROM TOP 2ND CLIP FROM TOP
NEEDLE SIZE D36 D36
NEEDLE JET 270 270
SLIDE #50 #50
FLOAT HEIGHT 25MM 25MM
1994 GT16:WITH PHBL24 (24mm) CARB TESTED BY US AT 1993 NATS IN CO.&TX.

MAIN: 95
PILOT: 42 OR 45
NEEDLE: D36
NEEDLE CLIP: TOP OR 2ND DOWN
NEEDLE JET: 268
SLIDE: 40
FLOAT HEIGHT: 27mm

1994 JT25: WITH PHBL26 (26mm) SEA LEVEL TO 3,000 FEET.

MAIN: 95
PILOT: 36 (38 OK)

NEEDLE: D36
NEEDLE CLIP: 2ND FROM TOP
SLIDE: 50
FUEL SCREW: 3.5 TURNS OUT
FLOAT HEIGHT: ARMS IN LEVEL PLANE WITH FLOAT BOWL BASE (PARALLEL)

1995 JT16: SEE ABOVE SPECS FOR 1994 MODEL
1995 JT25: SEE ABOVE SPECS FOR 1994 MODEL
1995 JT35: WITH PHBL26 (26mm) SEA LEVEL TO 3,000 FEET.

MAIN: 98
PILOT: 38 (40 OK)
NEEDLE: D36
NEEDLE CLIP: 2ND FROM TOP
SLIDE: 50
FUEL SCREW: 3.5 TURNS OUT
FLOAT HEIGHT: ARMS IN LEVEL PLANE WITH FLOAT BOWL BASE (PARALLEL)

1996/1997 JTR270,JTX270: WITH PHBL26 (26mm) SEA LEVEL TO 3,000 FEET.

MAIN: 114
PILOT: 36 (38 OK)
NEEDLE: D36 (2nd CLIP POSITION DOWN FROM THE TOP)
SLIDE: 60
FUEL SCREW: 3.5 TURNS OUT
FLOAT HEIGHT: ARMS IN LEVEL PLANE WITH FLOAT BOWL BASE (PARALLEL)

1996/1997/1998 JTR370/JTX320/TX320: WITH PHBH26CS (OVAL PORT LARGE BODY DELLORTO) SEA LEVEL TO 3,000 FEET.

NOTE: THIS CARBURETOR DIFFERS FROM ALL OTHER DELLORTOS USED BY GASGAS. FOR BETTER PERFORMANCE, IT IS POPULAR TO CONVERT THESE MOTORCYCLES TO THE KEIHIN PWKGG28 (28mm) CARBURETOR AS SUPPLIED BY GASGAS SPAIN.

DELLORTO PHBH26CS (26mm OVAL PORT) SPECS:

MAIN: 115
PILOT: 45
NEEDLE: X18 (3rd CLIP POSITION DOWN FROM TOP)
SLIDE: 55
AIR SCREW: 1.5 TURNS OUT (NOTE: THIS IS AN AIR SCREW ON THIS MODEL)

KEIHIN PWKGG28 (28mm) CARBURETOR SPECS:

MAIN: 118 (120, 122, 125 OK)
PILOT: 48 (45 OK)
NEEDLE: CENTER POSITION OF FIVE. (THIRD DOWN FROM TOP)
SLIDE: 35
AIR SCREW: 1.5 TURNS OUT (NOTE: THIS IS ALSO AN AIR SCREW)

1998 TX270/1999 TXT270,TXT321/2000 TXT280,TXT321/2001 TXT280,TXT321/2002 TXT280 EDITION 02: WITH PHBL26 (26mm) SEA LEVEL TO 3,000 FEET

MAIN: 114
PILOT: 36 (38 OK)
NEEDLE: D36 (2nd CLIP POSITION DOWN FROM TOP)
FUEL SCREW: 3.5 TURNS OUT
FLOAT HEIGHT: ARMS IN LEVEL PLANE WITH FLOAT BOWL BASE (PARALLEL).

2000/2001/2002 TX50 Boy High altitude for 6000 FEET AND ABOVE.

MAIN: 64 (STOCK IS 70)
NEEDLE: (2nd CLIP POSITION DOWN FROM TOP)
TESTED AND VERIFIED BY EUROPEAN DIRT, Silt Colorado April 04 2001

2001 TXT80/2002 TXT70 "ROOKIE" WITH DELLORTO PHBG21DS (21mm) SEA LEVEL TO 3,000 FEET

(NOTE: THERE IS A SLIDE MODIFICATION BULLETIN. PURPOSE: TO CORRECT THROTTLE HESITATION JUST OFF OF IDLE. SEE YOUR DEALER OR RISING SUN IMPORTS FOR MORE INFORMATION) rsiinc@ffni.com

MAIN: 92 (JETS ARE SMALLER THAN USED IN PHBL CARBURETORS)
PILOT: 50
NEEDLE: W7 (CLIP IN TOP OR 2nd DOWN FROM TOP)
SLIDE: 40
AIR SCREW: 1.5 TURNS OUT (NOTE: THIS IS AN AIR SCREW)

2002 TXT280 PRO TXXI: WITH PHBL26 (26mm) SEA LEVEL TO 3,000 FEET

MAIN: 118 (115 OK, NOTHING SMALLER!)
PILOT: 36 (38 OK)
NEEDLE: D36 (2nd CLIP POSITION DOWN FROM TOP)
FUEL SCREW: 3.5 TURNS OUT
FLOAT HEIGHT: ARMS IN LEVEL PLANE WITH FLOAT BOWL BASE (PARALLEL)

ELECTRICAL INFORMATION

NOTE ABOUT THE COOLING FAN MOTOR: THE MOST COMMON PROBLEM IS "STALLING" OF THE MOTOR BLADE. TYPICALLY, THE MOTOR WILL RUN WHEN THE BLADE IS TAPPED WITH A FINGER. THIS IS A SIGN THAT THE ARMATURE HAS A SPOT (OR SPOTS) THAT ARE CORRODED. AS THIS MOTOR UNIT IS SEALED, REPLACEMENT IS THE ONLY REPAIR OPTION. THE MOST COMMON CAUSE OF FAILURE OF THE MOTOR ARMATURE IS PRESSURE WASHING. (THIS APPLIES TO ALL MAKES OF TRIAL BIKES FROM ALL MANUFACTURERS) SOAPY WATER IS INJECTED UNDER HIGH PRESSURE INTO THE ARMATURE CAUSING EVENTUAL CORROSION AND FAILURE. GASGAS FAN MOTORS ARE THE SAME FROM 1990 THROUGH 2002. WE RECOMMEND THAT PRESSURE WASHING BE AVOIDED IF POSSIBLE. IF NECESSARY TO PRESSURE WASH, AVOID AIMING THE WAND NEAR THE FAN MOTOR, AND OTHER ELECTRICAL COMPONENTS. AS WELL AS THE WHEEL BEARINGS, SUSPENSION LINKAGE, STEERING BEARINGS, ETC..
THE 1991 GT25 FLYWHEEL WEIGHT 2252.5 gr. 80.44 oz. (5.02 lbs.)
THE 1992 GT32 FLYWHEEL WEIGHT 2526.5 gr. 90.23 oz. (5.63 lbs.)
THE 1993 GT25T FLYWHEEL WEIGHT 2684.7 gr. 95.88 oz. (5.99 lBS.)
THE 1996/2001 KOKUSAN FLYWHEEL 3560.0 gr. 125.58 oz. (7.85 lbs.)
THE 91/92/93 GT25 MOTOPLAT IS A No.0612225
THE 91/92/93 (1993 GT25T TO APRIL 1993) GT25 MOTOPLAT BLACK BOX IS MOTOPLAT No.9635406
THE 92/93/94 GT16,JT16 (ALL GT25T/JT25 AFTER APRIL 1993) MOTOPLAT BLACK BOX IS No. 9635404

ON MOTOPLAT AND DUCATI SYSTEMS, THE BROWN/REDDISH (TERRA COTTA COLOR) ELECTRICAL BOX IS THE "FAN MODULE". IT'S SOLE PURPOSE IS TO CONVERT THE 12V AC CURRENT COMING FROM THE VOLTAGE REGULATOR TO 12V DC CURRENT FOR THE COOLING FAN MOTOR.

COMMENTS: VERY FEW FAILURES OF HAVE BEEN REPORTED.

ON MOTOPLAT AND DUCATI SYSTEMS THROUGH 1995, THE SILVER BOX IS THE "VOLTAGE REGULATOR". IT REGULATES THE CURRENT COMING FROM THE MAGNETO TO A CONSTANT 12V AC. IT'S MAIN PURPOSE IS TO PREVENT HIGH RPM VOLTAGE FROM DAMAGING LIGHT BULBS AND ELECTRICAL COMPONENTS.

COMMENTS: VERY FEW FAILURES HAVE BEEN REPORTED.

THE BLACK BOX IS THE "IGNITION REGULATOR". IT CONTROLS MANY FUNCTIONS OF THE IGNITION SYSTEM. THE ADVANCE/RETARD, THE TIMING, ECT.

COMMENTS: THIS IS USUALLY THE CAUSE OF MOST ELECTRICAL PROBLEMS INVOLVING THE SMOOTH RUNNING OF THE ENGINE. HOWEVER, VERY FEW FAILURES HAVE BEEN REPORTED. TYPICAL FAILURE SYMPTOMS ARE MISSFIRE AT HIGHER RPM AS THE ADVANCE IS NOT WORKING PROPERLY, OR THE MOTORCYCLE WILL NOT START. TO TEST, EXCHANGE FOR ANOTHER IDENTICAL COMPONENT UNIT AND TEST RUN ENGINE. IT IS NOT POSSIBLE TO RUN DIAGNOSTIC TESTS ON THIS COMPONENT. APPLIES TO ALL SYSTEMS FROM 1990 TO PRESENT.

THE IGNITION COIL (SPARK PLUG WIRE ATTACHES TO IT) IS MADE IN JAPAN BY VARIOUS MANUFACTURERS AND FAILURES ARE VERY RARE.

THE TIMING OF THE ENGINE IS AS FOLLOWS:1991/93 GT25 2.3mm BDTC

1991/93 GT32 2.0mm BDTC
1993/2001 GT16 0.7mm BDTC
1991 AIRE 250 2.7mm TO 3.0mm
1991 AIRE 327 2.4mm BDTC
1994/2001 (ALL) 2.7mm BDTC

ALTERNATIVE FOR SMOOTHNESS 1995/2001 338cc,327cc 2.4mm BDTC

ON BIKES MADE BEFORE APRIL 1994, (MOTOPLAT SYSTEM) SOME OF THE ENGINE ELECTRICAL PROBLEMS HAVE BEEN CAUSED BY POOR CONNECTIONS AND CRIMPING OF CONNECTORS. THE GROUND IS VERY IMPORTANT! THE MOTOPLAT IS A "NO CIRCUIT GROUND SYSTEM". THERE MUST BE A GOOD GROUND PATH BETWEEN THESE PARTS.(THE COIL AND STATOR GROUND BY THEIR MOUNT. THE BLACK BOX HAS A GROUND WIRE).THE BLACK BOX SHOULD BE GROUNDED DIRECTLY TO THE FRAME. THE MOUNT BOLT FOR THE SILVER VOLTAGE REGULATOR IS A GOOD GROUND PATH. THIS IS VERY IMPORTANT! SOME BIKES HAD THE BLACK BOX GROUNDED TO THE WATER OVERFLOW BOTTLE (1992/1993 MODELS). THIS CAUSED A PREMATURE FAILURE OF THE BLACK BOX. THE CHROME FRAME IS A GOOD GROUND BUT NOTE THAT THE ENGINE MOUNT AREAS MUST BE CLEAN UNPAINTED FOR THE STATOR GROUND TO PASS TO THE FRAME. SPARK PLUG CAPS THAT DO NOT FIT PROPERLY,OR ARE IMPROPERLY INSTALLED TO THE COIL WIRE. WATER IN THE IGNITION FROM IMPROPER SEALING OF THE MAG COVER. DEFECTIVE KILL BUTTON OR KILL BUTTON WIRE IS TOUCHING GROUND. (MANY TIMES THE KILL BUTTON IS THE CULPRIT! ALWAYS DISCONNECT THE KILL BUTTON AND TAPE OFF THE WIRE. TEST THE MOTORCYCLE FOR PROPER OPERATION BEFORE ADVANCING TO FURTHER ELECTRICAL DIAGNOSIS.)

TO TEST THE IGNITION STATOR OR IGNITION COIL WITH AN OHM METER (MOTOPLAT):
NIPPON DENSO COIL:

THE RED LEAD INSERTED IN THE SPARKPLUG CAP AND THE BLACK PROBE TOUCHING THE BODY OF THE COIL.RESULT:18K OHMS

THE RED LEAD TOUCHING THE MALE WIRE PLUG ON BODY OF COIL,THE BLACK WIRE TO GROUND ON THE BODY. RESULT:1.5 OHMS

MOTOPLAT STATOR:
UNPLUG THE BLACKBOX MODULE IN FRONT OF RADIATOR OVERFLOW BOTTLE.
GROUND THE BLACK PROBE ON YOUR OHMMETER.(CHROME FRAME IS GOOD GROUND)
HOLDING THE HARNESS PLUGIN FOR THE BLACKBOX:
INSERT THE RED PROBE INTO TERMINAL FOR THE BLACK WIRE.RESULT:35 OHMS
INSERT THE RED PROBE INTO TERMINAL WITH BLUE WIRE.RESULT:45 OHMS
INSERT THE RED PROBE INTO TERMINAL WITH YELLOW WIRE.RESULT:1 OHM

FOR DUCATI AND KOKUSAN SPECIFICATIONS, SEE THE OHM READINGS INCLUDED WITH THE WIRING DIAGRAMS AT: http://www.gasgas.com

SPARK KNOCK: THIS CAN RESULT FROM A NUMBER OF DIFFERENT CAUSES. LOW WATER LEVEL IN THE COOLING SYSTEM WILL CAUSE THE ENGINE TO RUN HOT AND DETONATION (SPARK KNOCK) WILL RESULT. THE COOLING FAN NOT OPERATING. FAILURE OF THE WATERPUMP. THE QUALITY AND AGE OF THE FUEL (MOST COMMON REASON). CARBON BUILD UP ON THE PISTON. CARBURETOR JETTING. DEBRIS BLOCKING THE FUEL JETS IN THE CARB. USING HIGHER GEARS AT LOW RPM. THE IGNITION TIMING OF THE STATOR. WORN PISTON PIN OR CONNECTING ROD BEARING HAS A SIMILAR SOUND.

TIMING NOTE: NO ONE HAS FOUND THEIR ORIGINAL FACTORY STATOR TIMING TO BE INCORRECT AS IT IS SET IN AN ALIGNMENT JIG DURING ENGINE ASSEMBLY.

GEARING OPTIONS FOR GAS GAS GT BIKES

REAR<SPROCKETS>FRONT NOTES: RATIO

WITH GT25&32 REAR SPROCKET:40TEETH 10T (OPTIONAL) 4.00/1
40T 11T (STOCK GT25&32) 3.63/1
40T 12T (OPTIONAL) 3.33/1
40T 13T (OPTIONAL) 3.07/1

WITH GT12&16 REAR SPROCKET:44T 10T (STOCK GT12&16) 4.40/1
44T 11T 4.00/1
44T 12T (OPTIONAL) 3.66/1
44T 13T (OPTIONAL) 3.38/1

BY RATIO:(LOWEST GEARING) 44T 10T (STOCK GT12&16) 4.40/1
44T 11T (SAME AS BELOW) 4.00/1
40T 10T (SAME AS ABOVE) 4.00/1
44T 12T 3.66/1
40T 11T (STOCK GT25&32) 3.63/1
44T 13T 3.38/1
40T 12T 3.33/1
(HIGHEST GEARING) 40T 13T 3.07/1