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Kawasaki FH721V Carburetor

Kawasaki FH721V - Fuel and Air Flow

The pilot system includes the pilot jet F, pilot screw G (Idle mixture screw), pilot air jet H, pilot outlet I, and the bypass holes J. The pilot system meters the fuel/air mixture while the engine is idling and running under a light load. Under these conditions there is very little air flow through the carburetor bore; so little that it is not enough to draw fuel through the main system of the carburetor and atomize it.

Instead, the fuel is drawn through the pilot system, since the nearly closed throttle valve K causes high speed air flow past the pilot outlet and bypass holes (even at low engine speed). Fuel flow in the pilot system is metered by the pilot jet. Air for better atomization is admitted via the pilot air jet in the mouth of the carburetor. The fuel/air mixture passes into the bore of the carburetor side stream of the throttle valve through the bypass holes and pilot outlet.

While the throttle valve is almost closed, it covers the small bypass holes opening into the bore from the pilot system. As the throttle valve begins to open, it uncovers the bypass holes, allowing more fuel/air mixture to flow. The extra flow is needed because the engine starts to run faster as the throttle is opened.

The pilot screw controls the amount of fuel/air mixture allowed through the pilot outlet, but does not meter the bypass holes. A moderate amount of air comes in around the throttle valve at an idle, so adjusting the pilot screw changes the fuel/air ratio. Turning the pilot screw (Idle mixture screw) out (Counterclockwise) enrichens the mixture; turning it in (clockwise) leans the mixture.

Kawasaki FH721V Carburetor Adjustment

Low Idle Speed Adjustment

- Disconnect all possible external loads from the engine.
- Start the engine and warm it up thoroughly.
- Adjust the low idle speed screw with Phillips Screwedriver until the engine idles at specified speed.
- Idle Speed (Carburetor idle rpm) - 1450 rpm.
- Release the throttle lever and adjust the low idle speed set screw on the control plate to obtain the specified governed low idle speed.
- Low Idle Speed (Governed idle rpm) - 1550 rpm.

High Idle Speed Adjustment

- High idle speed adjustment should be made after the idle speed adjustment is performed.
- Do not adjust high idle speed with the air cleaner removed.
- Start and warm up the engine thoroughly.
- Move the throttle lever at a dash to the high idle position and match the lever hole position with the panel hole by inserting 6 mm dia., pin or bolt.
- Loosen two M6 control panel mounting bolts enough to move the control panel assembly.
- Carefully move the control panel assembly right side up or down to obtain the specified high idle speed. High Idle Speed 3600 rpm.
- Tighten the M6 Mounting bolts. Torque - Control Panel Mounting Bolts: 5.9 Nm (52 in-lb).
- Remove the 6 mm dia., pin or bolt.
- Check the idle speed, and readjust the idle speed if necessary.

High Altitude Operation

- At high altitude, the standard carburetor air-fuel mixture will be excessively rich.
- Performance will decrease, and fuel consumption will increase.
- High altitude performance can be improved by installing a smaller diameter main-jet in the carburetor and correct idle speed.
- The main jet high altitude kits are available if the equipment is to be used in the high altitudes.
- The main jet numbers are stamped on ends of the main jets.

High Altitude Main Jet

Altitude 0-1000 m (0-3000 ft): Main Jet L: #136; R: #140.
Altitude 1000-2000 m (3000-6000 ft): Main Jet L: #133; R: #139.
Altitude 2000 m (6000 ft): Main Jet L: #130; R: #134.

Kawasaki FH721V Carburetor Disassembly and Assembly

1. Pilot Screw Plug, 2. Pilot Screw, 3. Low Idle Speed Screw, 4. Spring, 5. Seal, 6. Collar, 7. Throttle Valve, 8. Screws, 9. Throttle Shaft, 10. Choke Valve, 11. Choke Shaft, 12. Seal, 13. Float Valve, 14. Pin, 15. Float, 16. Gasket, 17. Float Chamber, 18. Screw, 19. Clamp, 20. Plug Main Jet, 21. Gasket, 22. Main Jet L, 23. Main Jet R, 24. Slow Jet, 25. Drain Screw, 26. Spring, 27. Gasket, 28. Solenoid Valve

Before disassembly, mark the out side of choke valve and throttle valves for assembling them. Replace the pilot screw (2) in accordance with the following procedure if necessary. Remove the pilot screw plug (material: Stainless steel) as follows: Punch a hole in the plug and pry it out with an awl or other suitable tool.

Turn in the pilot screw and count the number of turns until it seats fully but not tightly, and then remove the screw. This is to set the screw to its original position when assembling. Turn in the new pilot screw (2) fully but not tightly, and then back it out the same number of turns counted during disassembly.

Install a new pilot screw plug (1) in the pilot screw hole by pressing with the rod, and apply a small amount of a bonding agent to the circumference of the plug to fix the plug. Install the choke valve and throttle valve on the shaft as the out side mark of them facing out side, and apply a small amount of a bonding agent to the valve screw threads. Drive the float pin so that it’s big diameter side faces the throttle shaft lever side. The fuel inlet valve seat is pressed into the carburetor body and is not replacable. Assemble carburetor parts which recommended tightening torque.

Kawasaki FH721V Carburetor Cleaning

- Disassemble the carburetor.
- Immerse all the carburetor metal parts in a carburetor cleaning solution and clean them.
- Rinse the parts in water and dry them with compressed air.
- Do not use rags or paper to dry parts. Lint may plug the holes or passages.
- Blow air through the holes and fuel passages with the compressed air.
- All holes must be open. Assemble the carburetor.

Kawasaki FH721V - Fuel system Inspection

- Remove the air cleaner.
- Place a suitable container under the drain screw on the carburetor.
- Turn out the drain screw a few turns to drain the carburetor and check to see if water or dirt has accumulated in the carburetor.
- Tighten the drain screw. Torque - 2.0 Nm (18 in-lb).
- If any water or dirt is found, clean the carburetor, and fuel tank, and check the fuel filter.