Yamaha Outboard 2B/2C/2U Service Manual (P/N LIT-18616-01-31)

• Model coverage: Covers Yamaha 2B, 2C, and cover-marked 2U outboards. The manual identifies 2MH as the U.S. and Canadian name for the 2B.
• Serial identification: Applies to 2B (2U), approved model 6A1, from serial 173765 onward, and 2C, approved model 6F8, from serial 030425 onward.
• Factory publication: A 91-page PDF of Yamaha P/N 6A1-28197-Z5-11, first edition June 1995, with Yamaha Literature No. LIT-18616-01-31.
• Covers scheduled maintenance, fuel-tank and carburetor service, idle-speed adjustment, gear-oil service, lower-unit leakage testing, spark-plug inspection, anode care, and lubrication points.
• Details power-unit removal and repair, recoil-starter overhaul, flywheel magneto removal, reed-valve inspection, cylinder-head service, and crankshaft, piston, ring, and bearing work.
• Documents lower-unit and propeller removal, water-pump and impeller inspection, pinion and forward-gear service, bearing and bushing replacement, shimming, and backlash measurement.
• Includes 16 exploded assembly views and 16 matching removal and installation charts, plus ignition test diagrams, a system-wide trouble-analysis chart, and regional special-tool references.

Engine and Maintenance Overview

Yamaha prepared this factory service manual primarily for its dealers and trained mechanics. It assumes a basic understanding of mechanical and electrical principles, making it best suited to technicians and experienced owners who can safely use the specified measuring equipment and service tools.

The cover identifies the 2B, 2C, and 2U, while the internal model table explains that the 2B was sold as the 2MH in the United States and Canada. The serial-number table further identifies this model family as 2B (2U), approved model 6A1. Yamaha’s library label describes the publication as the 2(U-V) 1996 Service Manual, so it should not be treated as blanket coverage for 2002 or other later model years.

Fuel-system repair begins with removal and inspection of the integral fuel tank, fuel cock, filter element, and fuel hose. The carburetor section goes beyond external adjustment, providing complete removal and disassembly coverage for the float chamber, needle valve, main jet, main nozzle, throttle components, choke assembly, and idle-adjusting system. Inspection criteria and float-height adjustment are included.

For top-end and internal engine repair, the manual covers power-unit removal followed by the cylinder head, reed valve, crankcase, cylinder body, crankshaft, piston, rings, wrist pin, small-end bearing, and crankshaft bearings. Factory inspection procedures address cylinder wear, taper and out-of-round, piston-to-cylinder clearance, ring end gap and side clearance, crankshaft runout, bearing condition, and mating-surface preparation. Reassembly notes identify piston orientation, ring locating-pin alignment, bearing direction, sealant locations, and staged fastener tightening.

The recoil-starter chapter includes spiral-spring and sheave-drum removal, rope replacement, spring setting, pawl inspection, reassembly, and an operational check. Flywheel magneto work is supported by the specified holder and puller rather than improvised removal methods.

Lower Unit and Electrical Coverage

The drive specifications identify a forward-only, shear-pin propeller system with no clutch, an important distinction from outboards equipped with selectable forward, neutral, and reverse gearing. Lower-unit repair coverage includes gear-oil service, pressure leakage testing, lower-unit and propeller removal, water-pump housing and impeller inspection, pinion and forward-gear removal, oil-seal service, and lower-case disassembly.

Separate procedures cover forward-gear bearing extraction, drive-shaft bushing removal and installation, gearcase water-passage inspection, forward-gear shimming, and backlash measurement. The upper case, exhaust guide, water tube, tiller handle, swivel bracket, and clamp bracket also have dedicated exploded views and removal charts.

Electrical diagnosis centers on the CDI ignition system. The manual provides an electrical-component layout, a color-coded ignition-system diagram, spark-gap testing, spark-plug-cap inspection, ignition-coil and charge-coil resistance checks, stop-switch continuity testing, and a CDI resistance chart. Regional differences are noted for the Canada/Europe resistance-type spark-plug cap. The final trouble-analysis chart links operating symptoms to the carburetor, compression components, cooling passages, lower unit, bracket, and ignition system.

Specification and Data Preview

The specification tables distinguish the 43 cm³ 2B from the 50 cm³ 2C, along with their different cylinder dimensions, compression ratios, carburetor identification and jetting, piston data, and spark-plug applications. Additional reference data covers component-specific tightening torques, wear limits, clearances, gear-oil capacity, propeller applications, ignition timing, gear backlash, shim selection, and electrical test values.

Special-tool listings provide U.S./Canada numbers alongside the corresponding 90890-series numbers used in other markets. Examples include the flywheel puller YB-06117 / 90890-06521, lower-case pressure tester YB-03595 / 90890-06762, and backlash indicator YB-06265 / 90890-06265.

The manual cautions that steel wire can enlarge carburetor jets and seriously affect engine performance. It also warns against spinning crankshaft bearings with compressed air because the bearings can be damaged. Fuel handling, ignition spark testing, recoil-spring service, and lower-unit pressure testing should be performed in accordance with the manual’s workshop safety instructions.