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| Illustration 1 | g00676469 |
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High-pressure gas carburetor (1) Idle adjustment screw (2) Load adjusting valve (3) Throttle stop screw (4) Throttle lever (5) Throttle shaft slot | |
- Turn idle adjustment screw (1) counterclockwise for four rotations from the closed position.
- For initial setting of the Impco 200 carburetor, turn load adjusting valve (2) to the center between the "L" and the "R".
The "L" represents a lean fuel mixture. The "R" represents a rich fuel mixture.
- Disconnect the governor linkage at throttle lever (4).
- Turn screw (3) until the throttle closes. Then turn the screw in order to slightly open the throttle.
Contact of the throttle plate with the throttle stop will cause premature wear on the throttle plate and the throttle body. Keep the throttle plate slightly open for the minimum fuel position.
- Move the control lever for the governor to the minimum fuel position.
- Adjust the length of the linkage between the governor and lever (4).
Make sure that the throttle plate and the governor are in the minimum fuel position.
- Reconnect the linkage between the governor and lever (4).
- Start the engine and adjust throttle stop screw (3) for the low idle.
For more information on adjustment of the governor-to-carburetor linkage, refer to Specifications, "Governor Linkage".
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| Illustration 2 | g00676615 |
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Low-pressure gas carburetor (1) Throttle (2) Load adjusting valve | |
- Turn load adjusting valve (2) clockwise until the screw is fully closed. Be careful not to overtighten the load adjusting valve.
- Turn load adjusting valve (2) counterclockwise for 3.5 to 4 revolutions.
- Start the engine and check the exhaust oxygen.
| Tools Needed | Quantity | |
| 391-8170 | EMISSIONS ANALYZER TOOL GP - (Bluetooth Module) (1) | 1 |
| 393-0673 | EMISSIONS ANALYZER TOOL GP (1) | 1 |
| 1U-5470 | Engine Pressure Group | 1 |
| (1) | Either analyzer may be used. |
The load adjusting valve affects the air/fuel ratio. The valve determines whether the mixture is rich or lean. The following factors are influenced by the air/fuel ratio:
- Fuel consumption
- Engine power output
- Engine stability
- Engine component life
- Deterioration of lube oil
Generally, the air/fuel ratio which produces the lowest fuel consumption produces more nitrogen oxides (NOx). This level of NOx can cause rapid deterioration of the lube oil through nitration.
Richer air/fuel ratios reduce NOx levels. A rich air/fuel ratio will have the following effects on the engine:
- Increase in fuel consumption
- Increase in levels of carbon monoxide
- Increased exhaust temperature
- Reduced service life of valves
- Higher costs for treatment of exhaust emissions and for maintenance
A lean air/fuel mixture will have the following effects on the engine.
- Reduction in fuel consumption
- Reduced exhaust temperature
- Increase in levels of NOx
- Reduction in power output
- Increase in the tendency for misfiring of the engine
The most accurate method of adjusting the air/fuel ratio involves the use of an emissions analyzer. This method consumes the least amount of time as well. The measurement of free oxygen O2 in the exhaust gas is an indicator of air/fuel ratio. If optimum fuel consumption is of prime importance, an O2 level of one to two percent will be required. This setting requires close monitoring of oil performance. Oil change intervals may be reduced. For more information, see Application and Installation, LEKQ7254, "Lubrication Systems" and Operation and Maintenance Manual, SEBU6400, "Caterpillar Gas Engine Lubricant Recommendations".
Note: A dual fuel engine has a load valve for each fuel.
Adjustment Procedure With An Oxygen Meter
- Remove a plug from the exhaust elbow and install the oxygen sensor.
- Remove one of the plugs from the air inlet manifold. Connect a line from the opening to an absolute pressure gauge in the 1U-5470 Engine Pressure Group.
- Start the engine and run the engine at rated load. Allow five to ten minutes for the conditions to stabilize. Make sure that the throttle is not fully open. Reduce the load, if necessary.
For generator set engines, the load can be determined by the electricity that is generated.
For industrial engines, the load can be estimated by the inlet manifold pressure. For information on estimating the load, see Special Instruction, SEHS7341.
- Use the oxygen meter to check the O2 level.
If the O2 level is not at the desired setting, slowly adjust the load valve until the desired O2 level is achieved.
Regulator for the Exhaust Bypass
Adjustment of the regulator for the exhaust bypass affects the engines power by changing the inlet manifold air pressure.
After the desired level of exhaust O2 is reached, adjust the regulator in order to achieve the engines full load operation at the desired throttle setting.
For maximum efficiency and stability, use a throttle angle of approximately 70 degrees.
Use the following procedure to adjust the regulator:
- Stop the engine and allow the regulator to cool.
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The exhaust bypass valve cover is under spring compression. To prevent personal injury, use caution when removing the cover.
- Remove bolts (1) and cover (2).
- Inspect the condition of the parts. Make sure that the diaphragm is in good condition. Replace any worn parts.
- Use spacers (3) and shims (2) to adjust the compression on the spring.
The spacers are used for rough adjustments and the shims are used for fine adjustments.
If you remove any spacers and/or shims, you will increase the spring force. This action will increase the boost pressure.
If you add any spacers and/or shims, you will reduce the spring force. This action will reduce the boost pressure.
- Install cover (2) and bolts (1). Tighten the bolts to a torque of
55 ± 15 N·m (41 ± 11 lb ft) . - Check the engines full load operation at the desired throttle setting. If the results are not satisfactory, adjust the regulator again.
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Hot engine components can cause injury from burns. Before performing maintenance on the engine, allow the engine and the components to cool. |
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| Illustration 3 | g00810309 |
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(1) Bolt
(2) Cover (3) Spacer (4) Shim | |