1978 Suzuki SP370 Factory Service Manual (P/N SR-6500)

• Covers the 1978 Suzuki SP370, including its air-cooled SOHC single, kick-start system, wet-sump lubrication, wet multi-plate clutch, and 5-speed constant-mesh transmission.
• Follows engine repair from compression testing and powerplant removal through cylinder-head and valve work, cylinder and piston inspection, crankcase separation, transmission service, and lower-end reassembly.
• Details the Mikuni VM32SS carburetor, including removal, overhaul, fuel-level checking, float adjustment, dual throttle-cable setup, air-cleaner service, and EPA calibration restrictions.
• Provides ignition and charging-system diagnosis, contact-breaker and mechanical-advance checks, rectifier and regulator testing, switch continuity charts, lighting data, and a complete wiring diagram with a wire-color key.
• Handles front and rear wheel and drum-brake service, steering-head bearings, front-fork disassembly and seal replacement, rear swingarm bearings, the gas/oil rear shock, frame replacement, and cable and harness routing.
• Identifies the source as a Suzuki Motor Co., Ltd. factory service publication dated June 1978, code SR-6500, supplied as a 184-page PDF with troubleshooting tables, special-tool numbers, repair specifications, exploded assembly views, and disassembly flow charts.

This PDF reproduces Suzuki Motor Co., Ltd.'s June 1978 factory service manual for the SP370 and its 369 cc four-stroke engine. Suzuki identifies experienced mechanics as the primary audience, while also stating that apprentice and do-it-yourself mechanics can use the manual. Because the deeper repair work relies on model-specific pullers, installers, gauges, and electrical test equipment, it is best suited to readers who already have normal workshop skills and the required tools.

SP370 Model and Service Scope

Coverage is assigned by the SP370 model designation, not by a listed frame- or engine-number range. The manual illustrates where both serial numbers are stamped, but it does not cover the SP400 or other Suzuki models. Its U.S. emissions material applies to SP370 motorcycles produced after January 1, 1978.

The maintenance section supplies the factory schedule and procedures for the battery, cylinder-head and exhaust fasteners, foam air cleaner, cam-drive chain, valve clearance, spark plug, breaker points, ignition timing, engine oil and filter, carburetor idle speed, throttle and clutch cables, drive chain, drum brakes, tires, steering, and critical chassis fasteners.

Engine, Transmission, and Fuel-System Repair

The engine chapter begins with compression diagnosis and complete engine removal and installation, including engine-mount shimming and component-specific tightening data. Top-end coverage extends to valve-guide replacement, stem seals, valve-seat cutting, spring inspection, rocker arms, camshaft journals, cam timing, and chain-tensioner setup. Cylinder, piston, and ring sections provide inspection methods, service limits, rebore guidance, and oversize-part identification.

Lower-end repair includes the flywheel magneto, engine sprocket, clutch and primary drive, oil pump and strainer, kick-start mechanism, shift cam and forks, 5-speed transmission, crankcase splitting, and crankshaft removal and installation. Inspection data covers runout, backlash, clearances, wear limits, oil-pump condition, and an engine oil-pressure test.

The VM32SS section explains its starter, main-metering, idle, and float circuits before moving into removal, overhaul, inspection, reassembly, and fuel-level adjustment. The EPA chapter identifies the close-tolerance main, needle, and pilot jets and warns against substituting standard jets. It also explains why the factory-set air and pilot screws are not routine service adjustments.

Electrical, Chassis, and Visual References

Electrical coverage includes the magneto ignition, coil, plug, advance governor, points, condenser, half-wave charging system, battery, voltage regulator, switches, horn, and lighting circuits. Troubleshooting tables isolate hard starting, rough running, overheating, abnormal engine noise, weak or absent spark, charging faults, steering problems, suspension complaints, and poor or dragging brakes.

Chassis procedures handle wheel and brake disassembly, bearing and axle checks, sprocket and chain inspection, handlebar controls, steering races, fork oil-seal and damper service, swingarm bearings, and frame replacement. Key visual references include the full wiring diagram, charging-system schematic, SP370 lubrication diagram, and disassembly flow charts for engine overhaul, carburetor assembly, and front fork. Numbered exploded views identify component names and assembly relationships rather than serving as a replacement-parts catalog.

The special-tool section lists Suzuki numbers, including crankshaft installer 09910-32812, crankshaft remover 09920-13111, compression gauge 09915-64510 with adapter 09915-63210, and front-fork oil-seal installer 09940-53111.

Assembly Cautions

The manual warns that tightening the cylinder-head cover while the tachometer driven gear is installed can break the cover. It also calls for the specified crankshaft puller and installer rather than hammering the crankshaft, since impact can disturb crankshaft alignment.

Fuel-system work, brake repair, engine removal, and the high-pressure nitrogen rear shock require correct support, clean working practices, and suitable shop equipment. Follow the factory cautions and use qualified assistance whenever the job exceeds your tools or experience.