1959-1969 Harley-Davidson Sportster K KH XLH XLCH Complete Service Manual

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Model HD, M, MV, and DC Carburetors Book

•    Carburetor maintenance

•    Motorcycle carburetor guide

•    Harley-Davidson carburetors

•    Vintage motorcycle carburetor

•    Carburetor troubleshooting

•    Model HD carburetor

•    Model M carburetor

•    Model MV carburetor

•    Model DC carburetor

•    Servi-Car carburetor

•    Carburetor adjustment

•    Carburetor fuel metering

•    Throttle body assembly

•    Idle speed setting

•    High-speed fuel jet

•    Carburetor cleaning

•    Carburetor disassembly

•    Carburetor rebuild kit

•    Fuel system troubleshooting

•    Throttle shaft replacement

•    Carburetor tuning

•    Fuel mixture adjustment

•    Idle needle valve adjustment

•    High-speed needle setting

•    Accelerator pump function


The document provides a detailed description of the Model HD carburetor, its components, operation, and maintenance procedures. It explains fuel flow regulation, acceleration, idle operation, and high-speed performance. Additionally, it includes troubleshooting steps, adjustment guidelines, and disassembly instructions for servicing and repairs.

Model HD Carburetor Overview

•    Dual-venturi, diaphragm-type carburetor with automatic economizer and accelerating pump.

•    Fuel supply control operates at any tilt angle and resists vibration.

•    Accelerating pump uses a plunger-type pump for extra fuel during acceleration.

•    Automatic economizer enriches fuel mixture at low speeds, prevents over-rich mixture at high speeds.
Operation and Adjustment

•    Starting: Choke closed, throttle slightly open, fuel enters metering system via engine suction.

•    Idle operation: Throttle slightly open, fuel flows through idle and intermediate channels.

•    Acceleration: Positive-action accelerating pump delivers fuel through boost venturi.

•    High-speed operation: Increased fuel flow from nozzle outlet ensures efficiency.

•    Carburetor adjustment: Minor tuning needed; check air cleaner and manifold for leaks.

•    Fine-tuning: Adjust low-speed and intermediate needles for optimal mixture.
Troubleshooting & Maintenance

•    Common issues: Check accelerator pump, clean passages, test valves, and inspect diaphragms.

•    Carburetor flooding: Clean inlet needle, adjust control lever, inspect diaphragm installation.

•    General operation checks: Ensure no air leaks, clean filters, and adjust inlet control lever.

•    Cleaning: Use compressed air to clear blocked channels and replace worn parts.

•    Model HD Carburetor: A dual-venturi, diaphragm-type carburetor with an automatic economizer and accelerating pump.

•    Fuel Regulation: Maintains fuel supply at any tilt angle, preventing poor fuel-air mixture or flooding.

•    Accelerating Pump: Uses a plunger pump to provide extra fuel for acceleration.
•    Automatic Economizer: Controls fuel mixture at low speeds and prevents over-rich mixtures at higher speeds.

•    Starting Operation: Choke is used for cold and warm engine starts to regulate fuel flow.

•    Carburetor Adjustment: Adjusting needles fine-tune fuel mixture for different speeds and conditions.

•    Common Issues & Fixes: Includes flooding, lean/rich mixtures, and faulty components like check valves and diaphragms.

•    Maintenance: Regular cleaning of fuel strainer and air cleaner ensures proper function.

Chapters Index - Model HD, M, MV, and DC Carburetors
1. Model HD Carburetor

•    Description & Function: Dual-venturi, diaphragm-type carburetor with economizer and accelerating pump.

•    Fuel Metering: Maintains fuel flow balance and operates at any tilt angle.

•    Accelerating Pump: Positive-acting plunger pump connected to throttle shaft.

•    Automatic Economizer: Controls fuel mixture at low speeds, preventing over-rich conditions.

•    Starting Operation: Uses choke and throttle adjustments for optimal fuel intake.


•    Idle Operation: Throttle shutter slightly open, exposing mixing passage to engine suction.

•    Acceleration & High-Speed Operation: Uses accelerating pump and economizer valve for fuel delivery.

•    Carburetor Adjustments: Fine-tuning of speed needles and throttle stop screw.

•    Common Issues & Troubleshooting: Covers flooding, lean/rich operation, and air leaks.

2. Model M Carburetor

•    Description: Plain tube carburetor with venturi and discharge nozzle.

•    Fuel Metering: Uses two jets for low and high speed adjustments.

•    Adjustments: Requires minor tuning for air-fuel mixture based on weather conditions.

•    Disassembly & Cleaning: Includes step-by-step removal and inspection procedures.

•    Reassembly & Calibration: Ensures proper float and throttle shaft alignment.

3. Model MV Carburetor

•    General Overview: Used in 1966 and later Servi-Car models.

•    Fuel Flow: Fuel enters through inlet connection and passes through main nozzle.

•    Idle & Slow Speed Operation: Fuel passes through idle tube for low-speed performance.

•    Disassembly & Cleaning: Step-by-step process for removing and inspecting parts.

•    Reassembly & Adjustments: Ensures proper float level and throttle settings.

4. Model DC Carburetor

•    Structure & Components: Consists of throttle body, carburetor body, and bowl assembly.

•    Disassembly & Cleaning: Includes removal of throttle shaft, float, and jets.

•    Reassembly & Calibration: Ensures correct float setting and throttle disc alignment.
5. Additional Components & Maintenance

•    Fuel Strainer: Traps dirt and water, requires periodic cleaning.

•    Air Cleaner: Prevents dust from entering the carburetor and engine.

•    Fuel Shut-Off Valve Alignment: Requires specific tool for proper installation.

Top 10 Questions Answered in This Book

•    How does the Model HD carburetor regulate fuel flow?
    
•    Uses a diaphragm-controlled inlet needle to maintain fuel balance.

•    What is the purpose of the accelerating pump?
    
•    Provides extra fuel for acceleration using a spring-loaded plunger.

•    How does the automatic economizer function?
    
•    Adjusts fuel mixture based on venturi airflow to prevent over-rich conditions.

•    What happens during the starting operation of the carburetor?
   
•    Choke closes, engine suction draws fuel into the mixing passage.

•    How is idle fuel supply maintained?
    
•    Fuel flows through idle channels, mixing with air before reaching the engine.

•    What adjustments can be made to the carburetor?
    
•    Low-speed and intermediate-speed needles control fuel mixture.

•    How is acceleration achieved in the carburetor?
    
•    A positive-action pump injects fuel into the boost venturi.

•    What are common causes of carburetor flooding?
    
•    Dirt in the inlet needle, incorrect diaphragm installation, or faulty inlet control lever.

•    How is high-speed fuel delivery managed?
    
•    Fuel flows through the main jet and economizer valve to the nozzle outlet.

•    What maintenance steps ensure carburetor performance?
    
•    Check accelerator pump, clean passages, inspect gaskets, and adjust fuel mixture.

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