Carb Specs

Original Sins, a/k/a/ Carb Specifications Consolidated: THE CHEAT SHEET:
"Information copyrighted and courtesy of XJ4Ever Inc., Atlanta, GA. www.xj4ever.com"

Here are all the different stock carb specs (carb model numbers, jet sizes, tune-up info, etc.) consolidated into one happy little group of information, so you can print this out easily when you are working on your particular set.

XJ550 Models:

Years & Models: 1981-83 XJ550 Maxim North American models
Carb Manufacturer: Mikuni
Carb Series: BS28
Carb Model ID: 5K500
Main FUEL Jet Size: #112.5
Pilot FUEL Jet Size: #35
Main AIR Jet Size: #70 (non-removable, in carb throat)
Pilot AIR Jet Size: #165
AIR COMPENSATOR Jet Size: not used.
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #4GN
Main needle JET Size: #O-8 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 2mm +/- 1mm (.08" +/- .039")
Idle RPM's: 1,200 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1981-83 XJ550 Seca North American models
Carb Manufacturer: Mikuni
Carb Series: BS28
Carb Model ID: 4U800
Main FUEL Jet Size: #112.5
Pilot FUEL Jet Size: #35
Main AIR Jet Size: #70 (non-removable, in carb throat)
Pilot AIR Jet Size: #170
AIR COMPENSATOR Jet Size: not used.
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #4GZ11
Main needle JET Size: #O-8 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 2mm +/- 1mm (.08" +/- .039")
Idle RPM's: 1,200 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1984 XJ550L Maxim models
Carb Manufacturer: Mikuni
Carb Series: BS32
Carb Model ID: 5K500
Main FUEL Jet Size: #105 (cylinders #1 & 2)
Main FUEL Jet Size: #102.5 (cylinders #3 & 4)
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #70 (non-removable, in carb throat)
Pilot AIR Jet Size: #155
AIR COMPENSATOR Jet Size: not used.
Starter FUEL Jet Size: #42.5 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #4CP7-3 (cylinder #2)
Main jet NEEDLE ID: #4CP3-3 (cylinders #1, 3, and 4)
Main needle JET Size: #N-8 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,200 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

XJ650 Models:

Years & Models: 1980-1 XJ650 Maxim, Midnight Maxim, and XJ650RJ Seca USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 4H700
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-10
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1980-1 XJ650 Maxim, Midnight Maxim, and XJ650RJ and RJC Seca Canadian models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 4H800
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-12
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1982-3 XJ650 Maxim USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 5N800
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #205
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-10
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1982-4 XJ650 Maxim Canadian models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 5N900 or 5U900
Main FUEL Jet Size: #112
Pilot FUEL Jet Size: #43
Main AIR Jet Size: #50
Pilot AIR Jet Size: #205
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-10
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1980-1 XJ650 4K0 and 4K1 models (UK/Europe)
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 4K000
Main FUEL Jet Size: #110
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #50
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: unknown
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-11
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1982-4 XJ650 11N models (UK/Europe)
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 5N900
Main FUEL Jet Size: #112
Pilot FUEL Jet Size: #43
Main AIR Jet Size: #50
Pilot AIR Jet Size: #205
AIR COMPENSATOR Jet Size: unknown
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-11
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1982 XJ650 14R models (UK/Europe)
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 5N900
Main FUEL Jet Size: #112
Pilot FUEL Jet Size: #43
Main AIR Jet Size: #50
Pilot AIR Jet Size: #225
AIR COMPENSATOR Jet Size: unknown
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-10
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1982-3 XJ650LJ/LK Turbo Seca North American models
Carb Manufacturer: Mikuni
Carb Series: BS30
Carb Model ID: 16G00
Main FUEL Jet Size: #127.5 (cylinders #1 & #4)
Main FUEL Jet Size: #132.5 (cylinders #2 & #3)
NOTE: the yamaha parts books reference the use of #125 main fuel jets. Original carbs that we have explored have the #127.5/#132.5 combination of jets as shown above.
Pilot FUEL Jet Size: #35
Main AIR Jet Size: #70 (non-removable, in carb throat)
Pilot AIR Jet Size: #170
NOTE: the yamaha parts books reference the use of #165 pilot air jets for the 1982 models, and #155 pilot air jets for the 1983 models. Original carbs that we have explored have the #170 jets as shown above.
AIR COMPENSATOR Jet Size: not used.
Starter FUEL Jet Size: #30 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #4DPS39
Main needle JET Size: #O-6, #318 style (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 2mm +/- 1mm (.08 +/- .04 inches)
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

XJ700 Models:

Years & Models: 1985-6 XJ700 air-cooled models
Carb Manufacturer: Hitachi
Carb Series: HSC33
1985 Carb Model ID: 1FG00 (N models) or 1JJ00 (NC models)
1986 Carb Model ID: 1NH00 (S models) or 1NK00 (SC models)
Main FUEL Jet Size: #107
Pilot FUEL Jet Size: #36.5
Main AIR Jet Size: #70
Pilot AIR Jet Size: #210
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #36 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-20
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 1.0mm +/- 1mm (.039" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1985 XJ700-X XN/XNC water-cooled USA models
Carb Manufacturer: Mikuni
Carb Series: BS33
Carb Model ID: 1AA00 (XN models) or 1FL00 (XNC models)
*Main FUEL Jet Size: #100 or #105
**Pilot FUEL Jet Size: #35 or 37.5
Main AIR Jet Size: #120 (non-removable, in carb throat)
Pilot AIR Jet Size: #140
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ82 (all except XNC model)
Main jet NEEDLE ID: #5FZ83 (XNC model)
Main needle JET Size: #Y-2 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3.0mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

NOTES:

  • there are discrepancies between the parts manuals and the service manual information on the size of the main fuel jets; one source claims these carbs were equipped with #100 main fuel jets, while other sources claim a #105 size main fuel jet.

** there are discrepancies between the parts manuals and the service manual information on the size of the pilot fuel jets; one source claims these carbs were equipped with #35 main fuel jets, while other sources claim a #37.5 size main fuel jet.

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.20mm (= 0.004" - 0.008")
Valve Clearance Exhaust: 0.21 - 0.30mm (= 0.008 - 0.012")

Years & Models: 1986 XJ700-X XS/XSNC water-cooled USA models
Carb Manufacturer: Mikuni
Carb Series: BS33
Carb Model ID: 1NW00 (XS models) or 1LT00 (XSC models)
Main FUEL Jet Size: #105
Pilot FUEL Jet Size: #35
Main AIR Jet Size: #120 (non-removable, in carb throat)
Pilot AIR Jet Size: #140
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ82
Main needle JET Size: #Y-2 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3.0mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.20mm (= 0.004" - 0.008")
Valve Clearance Exhaust: 0.21 - 0.30mm (= 0.008 - 0.012")

XJ750 Models:

Years & Models: 1981-3 XJ750 Maxim, Midnight Maxim, and Seca USA models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 15R00 (Maxim, Midnight Maxim)
Carb Model ID: 5G200 (Seca)
Main FUEL Jet Size: #120
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #80
Pilot AIR Jet Size: #225
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-13
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1981-3 XJ750 Maxim, Midnight Maxim, and Seca Canadian models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 15T00 (Maxim, Midnight Maxim)
Carb Model ID: 5H200 (Seca)
Main FUEL Jet Size: #120
Pilot FUEL Jet Size: #43
Main AIR Jet Size: #80
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: #36
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-14
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1981-4 XJ750 11M UK/Europe Seca models
Carb Manufacturer: Hitachi
Carb Series: HSC32
Carb Model ID: 5N100
Main FUEL Jet Size: #120
Pilot FUEL Jet Size: #43
Main AIR Jet Size: #80
Pilot AIR Jet Size: #195
AIR COMPENSATOR Jet Size: unknown if used.
Starter FUEL Jet Size: #40 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-14
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1983 XJ750E-II models
Carb Manufacturer: Hitachi
Carb Series: HSC33
Carb Model ID: 29R00
Main FUEL Jet Size: #105 (cylinders #1 & #4)
Main FUEL Jet Size: #102 (cylinders #2 & #3)
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #70
Pilot AIR Jet Size: #225
AIR COMPENSATOR Jet Size: not used.
Starter FUEL Jet Size: #43 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-17
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 5mm +/- 1mm (.197" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1984 XJ750RL Seca models
Carb Manufacturer: Hitachi
Carb Series: HSC33
Carb Model ID: 41Y00
Main FUEL Jet Size: #106
Pilot FUEL Jet Size: #40 or #41 (unsure which is correct)
Main AIR Jet Size: #70
Pilot AIR Jet Size: #225
AIR COMPENSATOR Jet Size: not used.
Starter FUEL Jet Size: #43 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #Y-18
Main needle JET Size: #3.2mm (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 1mm +/- 1mm (.039" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1985-6 XJ750-X XN/XS water-cooled Canadian models
Carb Manufacturer: Mikuni
Carb Series: BS33
1985 Carb Model ID: 1FL00 (XN models)
1986 Carb Model ID: 1MY00 (XS models)
Main FUEL Jet Size: #105
Pilot FUEL Jet Size: #37.5
Main AIR Jet Size: #120 (non-removable, in carb throat)
Pilot AIR Jet Size: #140
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ83
Main needle JET Size: #Y-2 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 3.0mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.20mm (= 0.004" - 0.008")
Valve Clearance Exhaust: 0.21 - 0.30mm (= 0.008 - 0.012")

XJ900 Models:

Years & Models: 1983-4 XJ900RK/RL and XJ900P Police models
Carb Manufacturer: Mikuni
Carb Series: BS35
Carb Model ID: 31A00
Main FUEL Jet Size: #102.5
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #45 (non-removable, in carb throat)
Pilot AIR Jet Size: #160
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #32.5 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #4HZ22 (900RK) or 4HZ26-3 (900RL and Police)
Main needle JET Size: #Y-0, style #318 (the main needle JET is also known as the "power valve" or "emulsion tube").
Float Valve Seat Size: 2.0mm, uses a longer float valve needle and the needle is not clipped to the float arm.
Fuel Level in float bowls: 5.0mm +/- 1mm (.197" +/- .039")
Idle RPM's: 1,100 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: XJ900 model 58L
Carb Manufacturer: Mikuni
Carb Series: BS36
Carb Model ID: 58L00
Main FUEL Jet Size: #107.5
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #45 (non-removable, in carb throat)
Pilot AIR Jet Size: #160
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ62-3
Main needle JET Size: #Y-0, style #318 (the main needle JET is also known as the "power valve" or "emulsion tube").
Float Valve Seat Size: 2.3mm, uses a shorter float valve needle and the needle is clipped to the float arm.
Fuel Level in float bowls: 5.0mm +/- 1mm (.118" +/- .039")
Idle RPM's: 1,050 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1984-90 XJ900 models 2HL, 3NG1, 3NG2
Carb Manufacturer: Mikuni
Carb Series: BS36
Carb Model ID: various
Main FUEL Jet Size: #107.5
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #45 (non-removable, in carb throat)
Pilot AIR Jet Size: #160
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ62-3
Main needle JET Size: #Y-0, style #318 (the main needle JET is also known as the "power valve" or "emulsion tube").
Float Valve Seat Size: 2.3mm, uses a shorter float valve needle and the needle is clipped to the float arm.
Fuel Level in float bowls: 5.0mm +/- 1mm (.197" +/- .039")
Idle RPM's: 1,100 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

Years & Models: 1991-4 XJ900 models 4BB1, 4BB2
Carb Manufacturer: Mikuni
Carb Series: BS36
Carb Model ID: various
Main FUEL Jet Size: #100
Pilot FUEL Jet Size: #40
Main AIR Jet Size: #45 (non-removable, in carb throat)
Pilot AIR Jet Size: #160
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #35 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5FZ10-3
Main needle JET Size: #Y-0, style #318 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 5.0mm +/- 1mm (.197" +/- .039")
Idle RPM's: 1,100 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm ( = 0.004 - 0.006")
Valve Clearance Exhaust: 0.16 - 0.20mm (= 0.006 - 0.008")

XJ1100 Models:

Years & Models: 1982 XJ1100 models
Carb Manufacturer: Mikuni
Carb Series: BS34
Carb Model ID: 10M00
Main FUEL Jet Size: #112.5
Pilot FUEL Jet Size: #47.5
Main AIR Jet Size: #140 (non-removable, in carb throat)
Pilot AIR Jet Size: #170
AIR COMPENSATOR Jet Size: not used
Starter FUEL Jet Size: #25 (non-replaceable, in float bowl)
Main jet NEEDLE ID: #5GLZ-34
Main needle JET Size: #X-2 (the main needle JET is also known as the "power valve" or "emulsion tube").
Fuel Level in float bowls: 5.0mm +/- 1mm (.197" +/- .039")
Idle RPM's: 1,100 rpms

Although not part of your carbs, your valve clearances should be considered as part of your "intake system", so here are those specs, too. Note that valve clearances should be measured with the engine "cold", meaning 70-degrees Fahrenheit or less:

Valve Clearance Intake: 0.11 - 0.15mm (= 0.004" - 0.006")
Valve Clearance Exhaust: 0.21 - 0.25mm (= 0.008 - 0.010")

If you're going to be getting fancy and modifying your intake or exhaust system, then you're going to be spending a lot of time re-tuning (re-jetting) your carbs in order to attempt to get them to run properly……and thus all the jetting size information from the above lists becomes somewhat useless (all the other specs will still be valid, though). Here's a few insights:

WHAT ABOUT RE-JETTING FOR PODS, ETC?:

It's a question we get asked often and unfortunately, one that we cannot answer honestly about your specific bike besides with "it depends".

Which is a nice way of saying "you're about to enter the seventh circle of hell……."!

Carb jet tuning required by aftermarket modifications is somewhat of a black art, part science, part skill, part luck. It depends on the current state of tune of your engine, your altitude, the mix of aftermarket parts on your bike, etc……..a lot of variables.

The best advice we can offer is: Just Say No. Don't do it! Leave everything stock!

But, since most people-with good reason, I might add-don't always listen to our well-intentioned advice, then the next best recommendation we can offer is: "if you want more power get a bigger bike!".

And since that doesn't cut it with many owners, either, for the remaining stalwarts out there who insist on "experimenting" with aftermarket intake and exhaust systems, here's the best information that we've come across to give you some GUIDANCE, which you should take as just that, and not as ANSWERS, because it isn't!

MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:

Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

or

+4 main fuel jet sizes for 4-into-1 exhaust

or

+4 main jet sizes for no muffler (open headers)

Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

or

+2 main fuel jet size for drilling holes in the airbox with stock filter

or

+4 main fuel jet sizes for individual pod filters (no airbox)

Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.

PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level.

PRECAUTIONS:

- Make sure your carbs are in perfect working order before making ANY jet changes….meaning fully cleaned internally and rebuilt, operating properly in their stock configuration, proper sized air jets and needles, etc. Otherwise, you'll like find that all of your efforts are going to be a HUGE waste of time.

- Check plug color often and adjust as needed, 2 main fuel jet sizes at a time and 1 pilot fuel jet size at a time. Bright white plug insulators are a sign of an overly lean fuel mixture condition and WILL cause damage to your engine over time, up to and including engine seizure!

- Synch the carbs after each jet change.

- Make sure the floats are set correctly

- Seriously consider purchasing a Colortune Plug Tuning kit.

- You may find it necessary to make changes to the size or shimming of the main jet needle. There are no guidelines on what or how to do these changes, this is true trial-and-error tuning!

EXAMPLE:

A 1982 XJ750RJ Seca using an aftermarket Supertrapp 4-into-1 exhaust and a single K&N air filter in the stock, unmodified airbox. Bike is primarily operated at an altitude of 2600 feet above sea level.

XJ750 Seca Stock Hitachi HSC32 Carb Jetting:

#120 Main Fuel Jet
#40 Pilot Fuel Jet
#50 Main Air Jet
#225 Pilot Air Jet
Y-13 Needle

MAIN FUEL JET SIZE CALCULATIONS:

Changes made:

Exhaust:
4 into 1 with Supertrapp = +4 Sizes Main Fuel Jet

Intake:
K&N Pod Filters = +4 sizes Main Fuel Jet


Equals: +8 main fuel jet sizes above baseline
Subtract: -2 main fuel jet size per formula above


Equals: +6 main fuel jet sizes due to modifications, thus:

Stock main fuel jet size is: #120

6 additional sizes

a #126 main fuel jet size


Subtract: -2 main fuel jet sizes for Altitude of 2500' Average

#126 calculated from above

-2 jet sizes for altitude adjustment

a #124 main fuel jet size.

PILOT FUEL JET SIZE CALCULATIONS:

The formula is: +1 pilot jet size increase for every +3 main jet sizes increased.

Stock pilot fuel jet size is: #40

2 additional jet sizes (since we went up +6 main fuel jet sizes before the altitude compensation was factored in):

a #42 pilot fuel jet size.

Note that no altitude compensation is needed on the pilot fuel jet since our elevation is less than 6000' a-s-l.


RESULT:

A #124 Main and #42 Pilot is A GOOD STARTING POINT.

**

Note that the above calculations do NOT take into account any possible changes in the sizes of the main or pilot air jets, the main needle or main needle jet size, and thus are additional variables and opportunities for tuning excellence. These are areas which are largely unexplored by most tuners, but logically should allow for additional fine tuning or additional rage and frustration………

Normally, changing to an aftermarket exhaust does NOT require re-jetting, (or minimal re-jetting) as almost ALL of the airflow restriction in the airflow path thru the engine (meaning: ATMOSPHERE > AIRBOX > FILTER > AIRBOX BOOTS > CARBS > INTAKE MANIFOLDS > CYLINDER HEAD PASSAGES > EXHAUST SYSTEM > BACK OUT INTO THE ATMOSPHERE) is within the intake side of this air flow path, and primarily within the stock airbox/air filter. Your stock EXHAUST system can already flow more air volume than the stock INTAKE system allows.

Thus changing only the stock EXHAUST system, with no changes to the intake side of the heads, normally makes NO DIFFERENCE IN TOTAL AIRFLOW, and "no difference in total airflow" means "no difference in TOTAL FUEL FLOW" either, and thus bigger jets are not needed.

But once you start freeing up the INTAKE side of the entire system, you will produce more system airflow, even with a stock exhaust system (because, the stock exhaust system has the capability to flow more air through it than what the stock intake system allows).

This is why re-jetting is usually needed even if you keep the stock airbox and the stock exhaust, but use a K&N low-restriction filter, or even if you drill holes in the stock airbox, or leave the filter lid off.

All such actions free up the intake side airflow restrictions; the stock exhaust will move this additional airflow, and without providing addition FUEL flow to match the increased airflow (within limits, an engine will gobble up the maximum amount of airflow that it can; an internal combustion engine is actually just a self-powered AIR PUMP) then the engine will run "lean"—-meaning not enough fuel to match the amount of airflow that the engine can (and now will) gulp.

Most pod type filters allow for vastly increased airflow, and thus require fuel re-jetting, and although no one really talks much about it, probably also require AIR JET changes to match the additional fuel flow, but since no one likes to deal with two parameters at once, it becomes a "tuning nightmare".

BUT, when you read all of the common symptoms of people who use pods, you quickly come to the conclusion that it's not possible to reproduce the stock "smooth in all rpm ranges" engine response. The reality is that you SHOULD be able to match it pretty darn closely, even with the increased airflow through the system, but ONLY changing the fuel jets isn't going to accomplish that. There are also air jets in the system, and they are there for a reason, as well as needle tapers and vacuum piston responsiveness issues.

For further insights and understanding, the Holy Grail (meaning: the whole miserable, un-varnished truth of what a real chore carb tuning is going to be, written by people who actually know what they're talking about, rather than by people who are trying to sell you something) can be found at:

www.factorypro.com

and then click on the "Product Support/Technical Support" link at the top of the page, then on the "Motorcycle Tuning Tech" link, and then the "CV Carb Tuning" link……..and then read, weep, study, and do….if you still dare to! HINT: if reading through it makes you think to yourself "sheesh, this sounds like an incredible amount of effort!", well, you're right! That's just some of the joys (and pitfalls) of getting to play "tuning engineer", which is what you're going to be doing. Yamaha probably has 10 of those types of guys on staff, and millions of dollars of test equipment, both physical and computer-aided, that allowed them to get the mixture settings just right-from an overall drivability AND power output standpoint—and now, since you're changing the airflow parameters thru the engine, you'll have to figure it all out "from scratch", but WITHOUT the benefit of 10 trained engineers and all that test equipment and experience.

That's why we warn you that setting up a bike for pods can be quite a bit of trial-and-error procedure. You can make the calculations according to what is shown in that guideline and then order the jets that the "formula" recommends, and that should serve as a good STARTING POINT…………you may (or may not!) have to do more tuning and trial-and-erroring substitution of different jet sizes, etc. to get it performing to you satisfaction, with the recognition that you may ALWAYS end up with a situation that has some kinds of trade-offs…..lazy at the lower end but runs well at mid/upper-ranges, or runs well at the lower end but a "flat-spot" at some other rpm range, etc. Unfortunately there is no magic formula……..you might want to read through the factorypro.com article that I list at the end of that section, and you will get a better understanding of what is involved to get the carbs set-up properly in a non-stock configuration.

As one of our favorite experts says about pod filters: "Get a Rubik's Cube instead…..it's less trouble and actually has an eventual solution!"

Revelations: JOURNALISM AT ITS FINEST!:

Graven Images Which Tell a Thousand Words:

Hitachi carb pictures and rebuild instructions, a big celebratory wheelie goes out to contributor Alive:

www.xjbikes.com/Forums…=3649.html

And a high-side Ole'! to Da'Schmuck for his exceptional Hitachi carb rebuild write-up:

mok.fileave.com/Hitach…akdown.pdf

Mikuni owners should also remember Alive in their nightly prayers:

www.xjbikes.com/Forums…=3690.html

Big Fitz gets medieval with his Valve Clearances, and shows how easy and important it is to actually get this task done on all air-head model engines:

xjbikes.com/Forums/vie…14827.html

and 85MaximXX takes you water-head owners by the hand, and leads you into the promised land of Valve Pad Replacement on those models:

www.xjbikes.com/Forums…16298.html

And the Fishmaster has a nice video of a vacuum diaphragm passing the CLUNK TEST with flying (or rather, "falling") colors:

xjmadness.myphotoalbum…clunk_test

And the reason you want your vacuum pistons to operate as closely as possible to no frictional resistance is because they must be able to do the following constantly, and if not, tuning and performance become troublesome or impossible:

www.youtube.com/watch?…re=related

Gamuru shows you how to clean that starter jet properly:

xjbikes.com/Forums/vie…=8918.html

And not to be outdone, Gamuru also shows how-to bench-synch a set of carbs using the easy, painless method:

xjbikes.com/Forums/vie…=6366.html

Definitely not Academy Award quality, but these two video presentations show a Colortune Plug in action:

www.gadgetjq.com/Vulca…e_Test.wmv

and

www.gadgetjq.com/Vulca…e_Test.wmv

and here's a few more:

going from orange (rich) to blue:

www.youtube.com/watch?…re=related

showing the blue to orange to blue changes:

www.youtube.com/watch?…re=related

showing a colortune being hooked up incorrectly (arcing):

www.youtube.com/watch?…re=related

Please remember, though, that a Colortune is NOT used to set your carbs at anything other than idle rpm's!!

And here's a great tutorial on using the Carbtune Synch Gauges:

www.youtube.com/watch?…re=related

SOME FINAL THOUGHTS:

Conclusions: A Few Observations That We Hope Are Now Self-Evident

a) If you don't plan on checking and correcting (if needed) the valve shim clearances, then don't bother cleaning and rebuilding the carbs.

b) If you don't plan on synching the engine when you're done, why bother cleaning and rebuilding the carbs?

c) If you don't plan on using a colortune plug to properly tune the carbs when you're done, what difference does it make whether they're clean and rebuilt?

d) You will never, EVER find anyone who is willing to do as thorough a job in cleaning your carbs as you are.

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