Onan JB Service Manual

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Onan JB Specifications

General

Engine Model	JB
Bore	3.25 inches
Compression Ratio	6.5:1
RPM	1800 RPM
Cooling	Air-Cooled
Fuel	Gasoline
Fuel System	Carburetor
Ignition System	Battery Ignition
Starting System	Electric Start
Fuel Type	Gasoline

Summary

Operators and Service Manual

Safety Precautions

General Safety Guidelines

Covers general hazards, moving parts, battery, fuel safety.

Specifications

Engine Specifications Table

Detailed technical data for JB and JC engines.

Dimensions and Clearances

Component Dimensions

Precise measurements for engine parts.

Tune-Up Specifications

Tune-Up Data

Specifications for adjusting engine performance.

Installation Procedures

General, Exhaust, and Fuel Installation

Gaseous Fuel System

Handling, Components, and Regulator

Engine Operation

Pre-Starting and Starting Procedures

Covers essential checks and steps for engine start.

Troubleshooting Guide

Engine Troubleshooting Chart

Guide to diagnosing common engine problems and causes.

Service and Maintenance

Periodic Service Chart and Notes A-E

Cooling System

Maintenance, Overheating, and Air Shutter

Fuel System

Gasoline Fuel System Overview

Gaseous Fuel Carburetion Systems

Fuel Pump and Strainer Service

Choke System Service and Adjustment

Operation, adjustment, and repair of the choke.

Gasoline Carburetor Description

Overview of the gasoline carburetor.

Combination Carburetor and Gaseous Fuel Regulator

Details on dual-fuel carburetor and gas regulator.

Ignition System

Maintenance, Testing, and Battery Ignition (JB)

Timing, Breaker Points, and Coil/Condenser

Procedures for timing, points, coil, and condenser.

Magneto and JC Ignition Systems

Governor System

Maintenance and Adjustments

Oil System

Maintenance, Gauge, Pump, and Filter Service

Starting System

Testing and Maintenance

Troubleshooting and upkeep procedures.

Starter Removal, Disassembly, and Pinion Gap

Flywheel Alternator System

Alternator Description and Maintenance

Charging System Testing and Troubleshooting

Procedures for testing and diagnosing charging issues.

Engine Disassembly and Repair

Cylinder Heads, Valves, and Adjustment

Compression Test and Cylinder Disassembly

Piston, Rod, and Valve Guide Service