GUIDE TO CARBURETOR JETTING

A BASIC GUIDE TO CARBURETOR JETTING

Proper carburetion is determined by your air/fuel mixture. The fuel flow in your carburetor is metered by the following components in this sequence:

1. Air screw and pilot jet

2. Throttle valve cutaway

3. Needle diameter (mm)

4. Needle L1 length (& clip position)*

5. Needle taper (in degrees)

6. Main jet

*These components may be replaced with a richer or leaner component.
*Each component controls fuel flow at a different throttle opening.

These components overlap each other depending on the particular throttle opening.

CARBURETOR JETTING COMPONENTS

Air Screw Controls air flow into the pilot jet circuit. Should be adjusted between 1 1/2 to
3 turns out. This affects throttle response right of idle.

Pilot Jet Controls fuel flow into the pilot jet circuit. Install one size richer or leaner pilot jet. This primarily affects idle through 1/4 throttle opening. Check response when riding out of turns.

Throttle Valve Cutaway Controls air flow into the venturi. Install one size larger or smaller cutaway. This primarily affects 1/8 to 1/3 throttle.

Needle
Diameter Controls fuel flow primarily at idle through 1/4 throttle. A smaller diameter needle is richer, allowing more fuel flow. A larger diameter is leaner, allowing less fuel.

Needle L 1 Length Controls fuel flow primarily at 1/4 to 3/4 throttle. A longer L 1 length is leaner and a shorter length is richer.

Needle Taper Controls fuel flow from 1/4 to full throttle. This has a major affect on jetting and generally does not need to be changed for fine tuning. More needle taper means progressively more fuel flow, or richer at full throttle. Less needle taper means there is less of an increase in fuel flow, or leaner at full throttle.

Main Jet Controls fuel flow primarily at 1/2 through full throttle. Increase or decrease one size at a time. Check spark plug color after a full throttle run. A medium brown indicates proper main jet size. Black means too rich. White or gray indicates a too lean condition.

A BASIC GUIDE TO CARBURETOR JETTING
Proper carburetion is determined by your air/fuel mixture.
The fuel flow in your carburetor is metered by the following components in this sequence:

1. Air screw and pilot jet

2. Throttle valve cutaway

3. Needle diameter (mm)

4. Needle L1 length (& clip position)

5. Needle taper (in degrees)

6. Main jet

These components may be replaced with a richer or leaner component.
Each component controls fuel flow at a different throttle opening.
These components overlap each other depending on the particular throttle opening.

--- -- --

The Contribution of Jetting Components Chart will give you an idea of how each
component affects fuel flow at various throttle openings.

CONTRIBUTION OF CARBURETOR JETTING COMPONENTS

Air Screw controls air flow into the pilot jet circuit. Should be adjusted between 1-1/2 to 3 turns out. This affects throttle response right of idle.

Pilot Jet controls fuel flow into the pilot jet circuit. Install one size richer or leaner pilot jet. This primarily affects idle through 1/4 throttle opening. Check response when riding out of turns.

Throttle Valve Cutaway controls air flow into the venturi. Install one size larger or smaller cutaway. This primarily affects 1/8 to 1/3 throttle.

Needle Diameter controls fuel flow primarily at idle through 1/4 throttle. A smaller diameter needle is richer, allowing more fuel flow. A larger diameter is leaner, allowing less fuel.

Needle L-1 Length controls fuel flow primarily at 1/4 to 3/4 throttle. A longer L-1 length is leaner and a shorter length is richer.

Needle Taper controls fuel flow from 1/4 to full throttle. This has a major affect on jetting and generally does not need to be changed for fine tuning. More needle taper means progressively more fuel flow, or richer at full throttle. Less needle taper means there is less of an increase in fuel flow, or leaner at full throttle.

Main Jet controls fuel flow primarily at 1/2 through full throttle. Increase or decrease one size at a time. Check spark plug color after a full throttle run. A medium brown indicates proper main jet size. Black means too rich. White or gray indicates a too lean condition.

Air Screw	Controls air flow into the pilot jet circuit. Should be adjusted between 1 1/2 to 3 turns out. This affects throttle response right of idle.
Pilot Jet	Controls fuel flow into the pilot jet circuit. Install one size richer or leaner pilot jet. This primarily affects idle through 1/4 throttle opening. Check response when riding out of turns.
Throttle Valve Cutaway	Controls air flow into the venturi. Install one size larger or smaller cutaway. This primarily affects 1/8 to 1/3 throttle.
Needle Diameter	Controls fuel flow primarily at idle through 1/4 throttle. A smaller diameter needle is richer, allowing more fuel flow. A larger diameter is leaner, allowing less fuel.
Needle L 1 Length	Controls fuel flow primarily at 1/4 to 3/4 throttle. A longer L 1 length is leaner and a shorter length is richer.
Needle Taper	Controls fuel flow from 1/4 to full throttle. This has a major affect on jetting and generally does not need to be changed for fine tuning. More needle taper means progressively more fuel flow, or richer at full throttle. Less needle taper means there is less of an increase in fuel flow, or leaner at full throttle.
Main Jet	Controls fuel flow primarily at 1/2 through full throttle. Increase or decrease one size at a time. Check spark plug color after a full throttle run. A medium brown indicates proper main jet size. Black means too rich. White or gray indicates a too lean condition.

Air Screw	controls air flow into the pilot jet circuit. Should be adjusted between 1-1/2 to 3 turns out. This affects throttle response right of idle.
Pilot Jet	controls fuel flow into the pilot jet circuit. Install one size richer or leaner pilot jet. This primarily affects idle through 1/4 throttle opening. Check response when riding out of turns.
Throttle Valve Cutaway	controls air flow into the venturi. Install one size larger or smaller cutaway. This primarily affects 1/8 to 1/3 throttle.
Needle Diameter	controls fuel flow primarily at idle through 1/4 throttle. A smaller diameter needle is richer, allowing more fuel flow. A larger diameter is leaner, allowing less fuel.
Needle L-1 Length	controls fuel flow primarily at 1/4 to 3/4 throttle. A longer L-1 length is leaner and a shorter length is richer.
Needle Taper	controls fuel flow from 1/4 to full throttle. This has a major affect on jetting and generally does not need to be changed for fine tuning. More needle taper means progressively more fuel flow, or richer at full throttle. Less needle taper means there is less of an increase in fuel flow, or leaner at full throttle.
Main Jet	controls fuel flow primarily at 1/2 through full throttle. Increase or decrease one size at a time. Check spark plug color after a full throttle run. A medium brown indicates proper main jet size. Black means too rich. White or gray indicates a too lean condition.