Kohler CH18, CH20, CH22, CH23, CH25, CH26, and CH730–750 Variants Command Horizontal Engine 1991–2007 Service Manual (P/N TP-2428-C)

• Covers Kohler Command CH18, CH20, CH22, CH23, CH25, CH26, CH730, CH740, CH745, and CH750 horizontal-crankshaft engines, with serial-number year-code identification from 1991 through 2007.
• Original Kohler factory service manual, Form No. TP-2428-C—a 232-page PDF issued in April 1992 and revised in March 2006.
• Carbureted-engine coverage includes the CH18-740 single-barrel Keihin and CH750 Keihin BK two-barrel systems, fuel-pump testing, carburetor repair, float inspection, and mechanical or electronic governor adjustment.
• LPG chapters cover liquid-withdrawal systems with Impco or Nikki carburetors and regulators, electric lock-off/filter assemblies, vaporizers, vacuum controls, component diagnosis, and qualified-service requirements.
• EFI service includes MA 1.7, MSE 1.0, and MSE 1.1 control systems, fuel-pressure diagnosis, sensor and injector testing, TPS initialization, governor setup, MIL blink codes, and a Bosch diagnostic flowchart.
• Full engine repair procedures take the CH-series through disassembly, dimensional inspection, cylinder and valve reconditioning, oil-pump service, camshaft and crankshaft setup, reassembly, ignition-module installation, and final adjustment.
• Electrical and accessory sections cover fixed-timing and SMART-SPARK™ ignition, regulated and unregulated charging systems, retractable starters, inertia-drive and solenoid-shift starter repair, and wet-disc clutch adjustment and reconditioning.

Engine Service and Technical Workflows

This is a factory workshop manual, not a basic operator’s guide. It is suited to professional small-engine technicians and experienced rebuilders equipped for leak-down, pressure, ignition, and electrical testing. Kohler expressly limits the LPG service section to qualified LPG service providers because that work requires specialized equipment and may be subject to licensing requirements.

The identification chapter explains how to read the engine’s Model, Specification, and Serial numbers, including letter suffixes and the newer combined model/specification format. Its specification tables distinguish the 624 cc CH22 build from the 674 cc CH22/23 version. They also separate the 725 cc CH25, CH26, and CH730-745 group from the 755 cc CH750, helping match internal repair data to the engine data plate.

General troubleshooting covers no-start, hard-starting, poor idle, misfire, overheating, knocking, power loss, oil consumption, and leakage complaints. Factory tests include crankcase-vacuum measurement and cylinder leak-down diagnosis. The overhaul chapters then address crankshaft and bearing-surface inspection, cylinder measurement and honing, valve-guide and valve-seat service, piston and ring inspection, connecting rods, hydraulic lifters, governor gear, pressure-relief valve, and gerotor oil pump.

Fuel and EFI Diagnosis

The EFI chapter treats the 35-pin MA 1.7 metal-cased ECU, 24-pin MSE 1.0, and 32-pin MSE 1.1 plastic-cased ECU as separate configurations. These control units and their harnesses are not interchangeable. Component-level test coverage includes the speed sensor, throttle-position sensor, oil-temperature sensor, oxygen sensor, relays, injectors, ignition coils, fuel pump, regulator, rail, and return circuit.

Fault-code tables identify the affected circuit, expected engine response, and likely sensor, harness, relay, or ECU causes. The Bosch EFI Diagnostic Flow Diagram links system-power, speed-sensor, fuel-pump, relay, ignition, injector-delivery, fuel-pressure, and base-engine checks. The manual also covers system priming, pressure relief, TPS synchronization after ECU or sensor work, and clearing stored fault codes.

Diagrams, Tools, and Repair Scope

Named illustrations include the CH18-740 carburetor exploded view, Keihin BK two-barrel carburetor exploded view, Bosch EFI Diagnostic Flow Diagram, capacitive-discharge ignition-module schematic, SMART-SPARK™ regulated charging-system wiring diagram, and wet-disc clutch exploded view.

The special-tools section identifies the EFI Service Kit 24 761 01-S, EFI diagnostic software 25 761 23-S, Cylinder Leakdown Tester 25 761 05-S, Oil Pressure Test Kit 25 761 06-S, and SMART-SPARK module tester 25 761 40-S, along with flywheel, starter, valve-guide, and hydraulic-lifter tools.

Several cautions are configuration-specific. Connecting or disconnecting an ECU harness with the ignition on can produce a voltage spike that damages the control unit, and the EFI fuel rail remains pressurized after shutdown. On Impco LPG carburetors, probing the calibrated load block can damage it, while disturbing the venturi orientation or preset throttle-shaft hardware can cause serious operating problems.

The LPG section provides system theory, troubleshooting, external tests, and general component service. Detailed internal regulator rebuilding and resetting instructions are supplied with the applicable repair kits rather than reproduced in this manual. Always isolate the ignition and battery before engine repair, relieve EFI fuel pressure before opening the system, and follow the manual’s precautions for rotating parts, gasoline, LPG, hot components, and spring-loaded starters.