Yamaha GPX338F & GPX433F Snowmobile Service Manual
This service manual is the workshop repair reference for the 1974 Yamaha GPX338F and GPX433F snowmobiles and their two-stroke, parallel-twin, air-cooled engines, running 66 pages of removal, disassembly, cleaning, inspection, assembly, and adjustment procedures. It's a true service manual — component-level teardown and repair across the engine, power train, chassis, and electrical systems — backed by service data, carburetor settings, and tightening-torque specifications. Originally published by Yamaha and delivered here as an instant PDF download you can read on any device or print for the bench.
Configurations covered: GPX338F (338 c.c.) · GPX433F (433 c.c.) — both covered together in this manual.
About the Yamaha GPX338F & GPX433F
The GPX338F and GPX433F were Yamaha's performance snowmobiles for the 1974 model year — in Yamaha's naming scheme of the era, the "F" suffix denotes 1974, succeeded by the GPX338G and GPX433G in 1975. Both are powered by two-stroke, five-port induction, natural air-cooled, aluminum-cylinder parallel-twin engines. The GPX338F displaces 20.62 cu. in. (338 c.c.) with a 2.362 × 2.346 in. bore and stroke, while the GPX433F displaces 26.42 cu. in. (433 c.c.) with a 2.677 × 2.346 in. bore and stroke. Both share a recoil hand starter, "Autolube" oil injection, flywheel magneto CDI ignition, a V-belt automatic transmission, and disc brakes.
The two sleds share a common chassis — a fabricated aluminum and steel frame, molded steel-reinforced rubber drive track, and 12V lighting — differing primarily in engine displacement and carburetion, with the GPX338F running twin Mikuni BN38-34SH diaphragm carburetors and the GPX433F running twin Keihin CDX42-38 units. Because these machines share so much, a single factory service reference covers both, and that combined documentation is exactly what keeps these vintage Yamaha snowmobiles running when parts and manuals get scarce.
What This Manual Covers
- General: Full specifications and service data for both the GPX338F and GPX433F, plus the special tools, gauges, general tools, and standard tools required to service the snowmobile.
- Engine removal: Step-by-step procedure for demounting the engine from the frame, including exhaust chamber, silencer, throttle and choke wire, and carburetor handling.
- Starter: Recoil hand starter parts breakdown and removal.
- Primary sheave: Disassembly, cleaning and inspection, assembly, and adjustment of the primary sheave, with special-tool callouts and V-belt wear limits.
- C.D.I. magneto: Removal and service of the flywheel magneto CDI ignition.
- Carburetor: Model-specific disassembly, cleaning and inspection, assembly, installation, and adjustment for both the Mikuni (GPX338F) and Keihin (GPX433F) carburetors, including the accelerator-pump carburetor on the GPX433F.
- Oil pump & engine: Autolube oil pump service and engine disassembly procedures.
- Power train: Secondary sheave removal, inspection, assembly, and adjustment; disc brake service; chain housing; front axle; rear axle; and sliding suspension.
- Steering (ski) and chassis: Frame, engine mount, oil and fuel, ski, steering, control wires, and shroud.
- Electrical system: Wiring and electrical component service across the CDI ignition and 12V lighting circuits.
- Tightening torque: Reference torque specifications for fasteners throughout the machine.
Why This Manual Matters
- Component-level repair, not just operation. This is a workshop service manual — it walks through tearing down and rebuilding the primary and secondary sheaves, carburetors, CDI magneto, oil pump, and engine, which is what you need when a repair goes past routine maintenance.
- Two models in one reference. Both the GPX338F and GPX433F are documented side by side, so the differences in engine, carburetion, jetting, and ignition are spelled out rather than assumed.
- The reference data the job depends on. Service data, carburetor jet and adjustment settings, spark plug specs, ignition timing, and tightening-torque figures are included, so you can reassemble to spec rather than guess.
- Two-stroke and clutch-specific procedures. Autolube oil pump stroke settings, V-belt wear limits, and primary/secondary sheave adjustments are all documented — the details generic guides don't carry.
- Vintage sleds, scarce documentation. Factory service literature for these early Yamaha GPX snowmobiles is increasingly hard to find — this PDF puts the complete manual back in your hands.
Manual Code: 878-28197-10