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Kohler CV490S Carburetor

Kohler CV490S engines are equipped with one of two basic types of fixed main jet carburetors: Walbro or Nikki.

Kohler CV490S Carburetor Troubleshooting

Problem - Engine starts hard, runs roughly or stalls at idle speed

Low idle fuel mixture/speed improperly adjusted. Adjust the low idle speed screw, then adjust the low idle fuel needle.

Problem - Engine runs rich (Indicated by black, sooty exhaust smoke, misfiring, loss of speed and power, governor hunting, or excessive throttle opening)

Choke partially closed during operation. Check the choke lever/linkage to ensure choke is operating properly. Low idle fuel mixture is improperly adjusted. Adjust low idle fuel needle. Float level is set too high. With fuel bowl removed and carburetor inverted, the exposed surface of float must be parallel with the bowl gasket surface of the carburetor body. Dirt under fuel inlet needle. Remove needle; clean needle and seat and blow with compressed air. Bowl vent or air bleeds plugged. Remove fuel bowl, low idle fuel adjusting needle, and welch plugs. Clean vent, ports, and air bleeds. Blow out all passages with compressed air. Fuel bowl gasket leaks. Remove fuel bowl and replace gasket. Leaky, cracked, or damaged float. Submerge float to check for leaks.

Problem - Kohler CV490S engine runs lean (Indicated by misfiring, loss of speed and power, governor hunting, or excessive throttle opening)

Low idle fuel mixture is improperly adjusted. Adjust low idle fuel needle. Float level is set too low. With fuel bowl removed and carburetor inverted, the exposed surface of float must be parallel with the bowl gasket surface of the carburetor body. Idle holes plugged; dirt in fuel delivery channels. Remove fuel bowl, low idle fuel adjusting needle, and welch plugs. Clean main fuel jet and all passages; blow out with compressed air.

Problem - Fuel leaks from carburetor

Float level set too high. Dirt under fuel inlet needle. Bowl vent plugged. Remove fuel bowl and clean bowl vent. Blow out with compressed air. Float is cracked or damaged. Replace float. Bowl retaining screw gasket damaged. Replace gasket. Bowl retaining screw loose. Torque screw to specifications.

Kohler CV490S Carburetor Adjustment

Carburetor adjustments should be made only after the engine has warmed up. The carburetor is designed to deliver the correct fuel to air mixture to the engine under all operating conditions. The main fuel jet is calibrated at the factory and is not adjustable.

The idle fuel adjusting needle is also set at the factory and normally does not need adjustment. Engines operating at altitudes above approximately 1830 m (6000 ft.) may require a special ‘high altitude’ main jet. If, however, the engine is hard-starting or does not operate properly, it may be necessary to adjust or service the carburetor.

Walbro Carburetor Adjustment

Engines may have a fixed idle or limiter cap on the idle fuel adjusting needle. Step 2 can only be performed within the limits allowed by the cap.

1. Start the engine and run at half throttle for 5 to 10 minutes to warm up. The engine must be warm before doing step 2.

2. Low Idle Fuel Needle Setting: Place the throttle into the "idle" or "slow" position. Turn the low idle fuel adjusting needle out (counterclockwise) from the preliminary setting until engine speed decreases (rich). Note the position of the needle. Now turn the adjusting needle in (clockwise). The engine speed may increase, then it will decrease as the needle is turned in (lean). Note the position of the needle. Set the adjusting needle midway between the rich and lean settings.

Nikki Carburetor Adjustment

Engines have the idle mixture preset and sealed at the factory. No adjustment is possible.

Low Idle Speed Setting

1. Start the engine and run at half throttle for 5 to 10 minutes to warm up. The engine must be warm before doing step 2.

2. Low Idle Speed Setting: Place the throttle control into the "idle" or "slow" position. Set the low idle speed to 1200 RPM (±75 RPM) by turning the low idle speed adjusting screw in or out. Check the speed using a tachometer. NOTE: The actual low idle speed depends on the application refer to equipment manufacturer's recommendations. The recommended low idle speed for basic engines is 1200 RPM. To ensure best results when setting the low idle fuel needle, the low idle speed must not exceed 1200 RPM (±75 RPM).

Kohler CV490S Carburetor Reassembly

- Install the low idle speed adjusting screw and spring.
- If removed during disassembly, install the low idle fuel adjusting needle and spring.
- Turn the adjusting needle in (clockwise) until it bottoms lightly.
- The tip of the idle fuel adjusting needle is tapered to critical dimensions.
- Damage to the needle and the seat will result if the needle is forced.
- Turn the low idle fuel adjusting needle out (counterclockwise) 1 turn.
- Insert the fuel inlet needle into the float.
- Lower the float/needle into the carburetor body. Install the float shaft.
- Install the bowl gasket, fuel bowl, bowl retaining screw gasket, and bowl retaining screw or fuel solenoid.
- Torque the bowl retaining screw to 5.1-6.2 Nm (45-55 in-lb.).

High Altitude Operation

When operating the engine at altitudes of 1830 m (6000 ft.) and above, the main fuel mixture tends to get overrich. An overrich mixture can cause conditions such as black, sooty exhaust smoke, misfiring, loss of speed and power, poor fuel economy, and poor or slow governor response.

To compensate for the effects of high altitude, a special high altitude main fuel jet can be installed. High altitude jets are sold in kits which include the jet and necessary gaskets. Refer to the Parts Manual for the engine being serviced for the correct kit number.

Fuel Shut-off Solenoid (Optional)

Some gasoline-fueled engines are equipped with the optional fuel shut-off solenoid, which is installed in place of the bowl retaining screw, to eliminate backfiring when the engine is shut down. If a solenoidequipped engine will not start, check whether sufficient voltage is reaching the solenoid.

A minimum of 7.3 volts DC is required to activate the solenoid. Also check to see that the ground lead from the carburetor body to the air cleaner base mounting stud is properly connected. If these check out, the solenoid should be removed for bench testing. Remember to shut off fuel supply and catch any fuel spilling from the carburetor as the solenoid is removed.

Bench test the solenoid by grounding the solenoid case and applying 12 volt DC to the spade terminal. If the plunger does not retract in this test, the solenoid is faulty and must be replaced. Always use a new fuel bowl gasket whenever the solenoid is installed.

Kohler CV490S - Fuel Pump

Some engines are equipped with an optional mechanical fuel pump. The fuel pump body is constructed of nylon. The nylon body insulates the fuel from the engine crankcase. This prevents the fuel from vaporizing inside the pump.

Operation

The mechanical pump is operated by a lever which rides on the engine camshaft. The lever transmits a pumping action to the diaphragm inside the pump body. On the downward stroke of the diaphragm, fuel is drawn in through the inlet check valve. On the upward stroke of the diaphragm, fuel is forced out through the outlet check valve.

Removal

- Disconnect the fuel lines from the inlet and outlet fittings of the pump.
- Remove the hex. flange screws, fuel pump, and gasket.
- If necessary, remove the fittings from the pump body.

Installation

Fittings - Apply a small amount of Permatex Aviation Perm-A-Gasket (or equivalent) gasoline resistant thread sealant to the threads of the fittings. Turn the fittings into the pump 5 full turns; continue turning the fittings in the same direction until the desired position is reached.

Install new gasket, fuel pump, and hex. flange screws. Make sure the fuel pump lever is positioned to the right of the camshaft (when looking at fuel pump mounting pad). Damage to the fuel pump, and severe engine damage, could result if the lever is positioned to the left of the camshaft.

Torque the hex. flange screws as follows: Into new as-cast hole - 9.0 Nm (80 in-lb.). Into used hole - 4.2-5.1 Nm (37-45 in-lb.). Connect the fuel lines to the inlet and outlet fittings.