Suzuki GN400 Supplementary Service Manual (P/N SR-6600)

• Factory identity and scope: Official Suzuki GN400 supplementary service manual, issued September 1980 as Part No. SR-6600 (英) E-01, SUPPL. 2. The 47-page PDF documents GN400 service data, procedures, and features that differ from the SP400 base model.
• Engine and drivetrain reference: Provides factory specification tables for the valve train, camshaft and cylinder head, piston/rings/cylinder, crankshaft, oil pump, clutch, transmission, and drive chain, with clearances, inspection limits, and test data.
• Carburetor coverage: Identifies the internal parts and factory settings of the Mikuni BS36SS, including the pilot circuit, jetting, float data, and the GN400 transient-enrichment system.
• Front brake repair procedures: Covers fluid-level checks, hydraulic-circuit bleeding, pad inspection and replacement, master-cylinder and caliper disassembly/reassembly, and brake-disc wear and runout testing.
• Steering and chassis work: Details steering-stem removal, bearing and race service, reassembly, adjustment, and final play checks; exploded assemblies and tightening data are supplied for the wheels, front fork, rear suspension, and related hardware.
• Market-specific electrical coverage: Includes dedicated wiring diagrams for the E-01/E-24, E-02, E-04/E-34, E-21, E-22, E-25, and E-28 versions, plus wire-routing, cable-routing, ignition, charging, lighting, and electrical test information.

Used alongside the SP400 service manual, this supplement is suited to experienced DIY owners and professional technicians who are already comfortable with hydraulic brake and front-end repair work and have access to the specified measuring and service tools. It is not a stand-alone replacement for the SP400 manual; unchanged base-model procedures are intentionally omitted.

Factory Repair Coverage

The front-disc-brake chapter goes well beyond a specification sheet. It documents pad wear inspection, pad replacement, system bleeding, master-cylinder removal and internal inspection, caliper piston and seal service, reassembly, and disc checks. Tool references include snap-ring pliers 09900-06108, micrometer 09900-20201, and dial gauge 09900-20808.

Steering-stem work is treated as a full front-end procedure. Coverage runs from component removal through bearing and race extraction, outer-race and lower-bearing installation, lubrication, reassembly, stem-nut adjustment, and the final check for free movement and bearing play. Suzuki identifies the required pullers, installers, and wrenches, including steering-stem nut wrench 09940-10122, bearing inner-race remover 09941-84510, steering race installer 09941-34511, and steering bearing installer 09941-74910.

The front and rear wheel, front fork, and rear suspension sections are primarily exploded-view and torque references. Buyers needing complete overhaul procedures for unchanged components will also need the base SP400 manual.

Variant and Service Data

The service-data section brings the GN400-specific engine, transmission, carburetor, electrical, brake, wheel, suspension, fuel, oil, tire-pressure, and lamp-wattage information together in one place. Rather than supplying only nominal specifications, many tables distinguish standard dimensions from service limits, allowing measured parts to be evaluated during repair.

Country codes are mapped directly in the manual: E-01 General, E-02 England, E-04 France, E-21 Belgium, E-22 West Germany, E-24 Australia, E-25 Netherlands, E-28 Canada, and E-34 Italy. The E-02 version receives separate entries for final gearing and chain length, wheel and tire fitment, fuel reserve, and front-fork oil level and capacity. Other market-dependent dimensions, lamps, spark plugs, and electrical details are identified under their respective codes.

Diagrams, Schematics, and Repair Cautions

Illustrated references include the BS36SS carburetor exploded view, transient-enrichment circuit diagram, front-brake master-cylinder and caliper assemblies, steering-stem bearing and special-tool drawings, market-specific wiring diagrams, and full-machine wire- and cable-routing layouts.

The brake chapter warns that mixing the specified glycol-based fluid with silicone- or petroleum-based fluid can cause serious component damage. It also cautions that excessive air pressure during caliper-piston removal can damage the piston. Brake and steering work should be performed with the motorcycle securely supported and with the factory hydraulic-system cautions observed.