Honda GB500 1989–1990 Factory Service Manual (P/N 61MK601)

This factory service manual covers the 1989–1990 Honda GB500 for the U.S. market, including standard and California emissions configurations. Honda's original 1989 edition is identified by P/N 61MK601. For the GB400 or XBR500, use the service literature for that model.

Finding Chapters and Reading the Wiring Diagram

Search, bookmarks, and wire labels: PDF text search is unavailable. Some chapter bookmarks open the wrong page, and the wiring bookmark does not reach the diagram. The full wiring diagram is on PDF p. 266. Small wire codes and connector labels need magnification, and a few remain hard to distinguish.

The ZIP contains one printable PDF with 272 pages, including the original cover, the safety notice, eight memo pages, one blank page, and 13 duplicate pages.

From Dry-Sump Service to Crankcase Repair

This selection of workshop topics focuses on maintenance, repair, and diagnosis. Honda also covers rear fender removal and exhaust pipe and muffler installation.

• Scheduled maintenance: Honda's maintenance schedule, oil-level and filter service, valve-clearance and compression checks, drive-chain adjustment, and brake and suspension inspections.

• Carburetor and emissions: Carburetor disassembly, cleaning, float inspection, and pilot-screw adjustment, plus secondary-air system inspection and California evaporative-emissions tests.

• Engine repair: Engine removal and installation, cylinder-head and valve repair, cam-chain timing, cylinder and piston inspection, crankcase separation, and crankcase bearing replacement.

• Clutch and drive: Clutch inspection, primary-drive gear service, kickstarter indexing, shift-linkage assembly, flywheel removal, and one-way starter-clutch repair.

• Chassis and brakes: Wheel, front fork, steering stem, rear shock, and swingarm service, plus rear drum-brake work and front hydraulic brake bleeding and overhaul.

• Electrical diagnosis: Battery and charging checks, CDI ignition testing, starter-motor and relay diagnosis, starting-interlock tests, and switch continuity charts.

• Factory reference data: Component torque tables, clearances, wear limits, fluid specifications, and fault-isolation charts for hard starting, loss of power, and poor low-speed or idle performance.

The manual assumes familiarity with standard workshop procedures and access to the tools specified for the job.

Dry-Sump Lubrication and Fuel System

The lubrication chapter traces the forced-pressure dry-sump oil circuit. It covers oil-tank removal, strainer and tank-screen cleaning, inspection of both sections of the oil pump, oil-line installation, and chassis lubrication points. The maintenance schedule refers to the separate owner's manual for the pre-ride inspection.

The carburetor chapter covers the vacuum piston, jet needle, float chamber, and air cut-off valve, with separate procedures for idle-drop and U.S. high-altitude adjustment. On California models, the purge-control valve tests and numbered vacuum-hose diagrams help identify the charcoal-canister plumbing before choosing parts or reconnecting hoses.

In-Frame Work and Engine-Out Repairs

The cylinder head, camshaft, rocker arms, sub-rocker arms, cam-chain tensioner, cylinder, and piston can be serviced with the engine in the frame. The head chapter includes valve-guide measurements, valve-seat contact checks and refacing, and timing views for reassembly.

Crankshaft, balancer, transmission, and crankcase bearing work requires engine removal and crankcase separation. The manual pairs transmission and balancer assembly drawings with shift-fork and connecting-rod clearance checks. That distinction helps plan labor, lifting support, bench space, and parts before teardown.

Honda explains how the half-decompressor and one-way decompressor can lift the right exhaust valve and give a false clearance reading. The crankcase chapter warns against prying at the mating surfaces and flags unusual resistance during assembly as a sign of misaligned parts.

Wheel, Suspension, and Brake Service

The chassis chapters detail wheel inspection, fork seal and bushing replacement, steering-head bearing and race service, shock disassembly, swingarm pivot bearing replacement, and drive-chain slider inspection. The brake procedures cover rear shoe and cam service, front pad and disc inspection, master-cylinder disassembly, and caliper piston and seal service.

Support the motorcycle securely before engine, wheel, fork, shock, or swingarm service. Let the engine and exhaust cool, and follow the manual's precautions for gasoline, battery electrolyte, brake dust, and hydraulic brake fluid.

Charging, Ignition, and Starter Circuits

The electrical chapters use harness-routing views, connector tests, and fault charts to trace charging and starting problems. They cover alternator and regulator/rectifier checks, pulse-generator diagnosis, ignition timing, side-stand and diode tests, and checks for the tachometer and brake and taillight warning sensor.

Identification and Special Tools

The model identification pages show the frame and engine markings, carburetor ID, and paint-code label. Honda lists the cam-chain tensioner holder 07973-MG30003, rotor puller 07733-0020001, fork-seal driver 07747-0010100, and shock-absorber compressor 07GME-0010000 so you can identify the tools before disassembly.

Valve Clearance and Ignition Test Examples

For cold valve-clearance checks, Honda specifies 0.10 mm (0.004 in) at the intake valves and 0.12 mm (0.005 in) at the exhaust valves.

The ignition inspection gives a pulse-generator coil resistance of 420–520 Ω at 68°F (20°C) for diagnosing weak or absent spark.