How to Clean the Carburetor on a 400EX

The TRX400EX was an all-terrain vehicle produced by Honda between 1999 to 2008. The 400EX used the same 397 cc, single-cylinder engine used by Honda's XR400 dirt bike, providing enough power to exhilarate most off-road enthusiasts. However, the 400EX's single carburetor is prone to clogging during extended periods of storage during the off-season. Clogs are formed as the fuel supply reduces to a green sludge that fills the carburetor's jets and fuel passages. All of the ATV's fenders and body panels must be removed to access the carburetor, which must then be disassembled for a thorough cleaning.

Things You'll Need

• 5 mm Allen wrench
• Phillips screwdriver
• 10 mm socket
• Socket wrench
• Pliers
• Gas can
• Flat screwdriver
• 12 mm open-end wrench
• 7 mm open-end wrench
• Container
• Carburetor cleaning solvent
• Aerosol carburetor cleaner
• Water
• Air compressor

Instructions

1. Park the ATV on a flat work space and set the parking brake. Let the engine cool for a minimum of 30 minutes.

2. Remove the seat and rear fender assembly, using the release lever under the right side of the seat. Lift the rear of the fender assembly upward, then pull it toward the rear of the ATV until it can be removed completely.

3. Unscrew the gas cap. Push down on the center of the gas tank cover trim clips, using the tip of a Phillips screwdriver. Pull all four clips out of the gas tank cover, then lift the cover off of the gas tank. Screw the gas cap into place.

4. Remove the side panels from both sides of the gas tank, using a 5 mm Allen wrench. Unscrew both bolts from the base of the front fender below the fuel tank, using a 5 mm Allen wrench. Remove the bolts from the bottom of both sides of the fender above the front wheels, using a 10 mm socket and a socket wrench. Slide the front fender toward the front of the ATV until it can be removed completely.

5. Turn the gas tank valve knob to the off position, then pull the fuel hose off of the valve outlet, using pliers. Unhook the mounting straps from the base of gas tank. Unscrew the mounting bolts from the front of the tank, using a 10 mm socket. Lift the gas tank off of the ATV.

6. Pull the carburetor drain hose, located at the bottom of the carburetor float chamber, free from the ATV's frame. Place the end of the hose into a gas can, then loosen the float bowl drain screw, using a flat screwdriver. Tighten the screw once all of the gasoline has drained from the carburetor.

7. Pull the breather hose off of the right side of the carburetor. Loosen the air box duct and engine intake clamps, located at the front and rear of the carburetor, using a Phillips screwdriver. Push the air box duct off of the carburetor, then pull the carburetor out of the engine intake.

8. Remove the throttle valve cover from the right side of the carburetor, using a Phillips screwdriver. Loosen the throttle cable lock nut, using a 12 mm open-end wrench, then remove the throttle cable and the cable end from the throttle valve. Pull the breather tube assembly off of the top of the carburetor.

9. Remove the air cut-off valve and spring from the right side of the carburetor, near the carburetor inlet, using a Phillips screwdriver. Remove the float chamber, accelerator pump cover, spring and diaphragm from the bottom of the carburetor, using a Phillips screwdriver.

10. Pull the baffle plate off of the central jet tower at the bottom of the carburetor. Remove the float and float pin, using a small punch, then lift the float valve out of its seat. Unscrew the main jet and needle jet holder from the central jet tower, using a flat screwdriver and a 7 mm open-end wrench. Unscrew the slow jet, located in the jet well forward of the central jet tower, using a flat screwdriver.

11. Turn the pilot screw, located under the carburetor outlet, clockwise with a flat screwdriver and count the amount of turns needed to lightly seat the screw against the carburetor body. Unscrew the pilot screw and remove its spring.

12. Place the pilot screw, main jet, slow jet, needle jet holder and float chamber in a container filled with carburetor cleaning solvent for a minimum of one hour. Remove the parts and rinse thoroughly with warm water. Blow compressed air through the jet nozzles and blow dry the parts.

13. Spray the carburetor's fuel and air passages with an aerosol carburetor cleaning spray, then blow compressed air through the passages. Repeat as needed until air can pass freely through all of the carburetor passages.

14. Reinstall the pilot screw and spring. Turn the screw clockwise until it seats lightly, then turn the screw counterclockwise the same amount of turns as it took to seat the screw in step 11. Reinstall the needle jet holder, main jet, slow jet, float valve, float, baffle plate and float chamber. Reinstall the accelerator pump diaphragm, spring and cover. Reinstall the air cut-off valve and spring.

15. Slip the throttle cable end into the carburetor throttle valve, then tighten the cable lock nut. Reinstall the throttle valve cover. Reattach the breather tube assembly to the top of the carburetor.

16. Reinstall the carburetor into the engine intake and push the air box duct onto the carburetor inlet. Tighten both clamps. Push the vent hose onto the nozzle on the right side of the carburetor.

17. Reinstall the gas tank, followed by the front fender, side covers and gas tank cover. Reinstall the seat and rear fender assembly onto the ATV.

Tips & Warnings

• Gasoline is flammable. Do not smoke or work near an open flame while servicing your ATV's fuel system.

• Wear protective gloves while working with carburetor cleaning solutions to avoid skin irritations.

References

• Honda TRX400EX Fourtraxx Service Manual; Honda Motor Company