14.9 Choke cable bracket (a) and screw (b)

1 Carburettor synchronisation is simply the process of adjusting the carburettors so they pass the same amount of fuel/air mixture to each cylinder. This is done by measuring the vacuum produced in each cylinder. Carburettors that are out of synchronisation will result in decreased fuel mileage, increased engine temperature, less than ideal

throttle response and higher vibration levels. Before synchronising the carburettors, make sure the idle speed is correct (see Section 2) and that the valve clearances are properly set (see Section 26).

2. 

   15.6 Fuel tap vacuum hose union on I cylinder inlet manifold (arrowed)

   To properly synchronise the carburettors, you will need a set of vacuum gauges or calibrated tubes (manometer) to indicate engine vacuum. The equipment used should be suitable for a two cylinder engine and come complete with the necessary adapter and hoses to fit the take-off points. Note: Because of the nature of the synchronisation procedure and the need for special instruments, most owners leave the task to a Honda dealer.

3. Start the engine and let It run until it reaches normal operating temperature, then shut it off.

4. Remove the fuel tank (see Chapter 4).

5. Displace the coolant hose and remove the blanking screw from the vacuum take-off point on the inlet manifold of No. 2 cylinder. Install the take-off adapter provided with the vacuum gauges.

6. Connect the vacuum gauge hoses to the inlet manifolds of both cylinders - the right gauge hose connects to the take-off adapter provided and the left gauge hose connects to the stub on the No. 1 cylinder manifold which the tap vacuum hose normally connects to (see illustration). Make sure they are a good fit because any air leaks will result in false readings.

7. Arrange a temporary fuel supply to the carburettors. Ensure the fuel supply is above the level of the carburettors.

Every 8000 miles 1.15

15.10 Carburettor synchronising screw (arrowed)

8. Start the engine and make sure the idle speed is correct. If it isn't, adjust it (see Section 2). If the gauges are fitted with damping adjustment, set this so that the needle flutter is just eliminated but so that they can still respond to small changes in pressure.

9. The vacuum readings for both cylinders should be the same, or at least within the tolerance listed in this Chapter's Specifications. If the vacuum readings vary, adjust the carburettors as follows.

10. The carburettors are adjusted by turning the synchronising screw situated in-between the carburettors on the throttle cable pulley (see illustration). Note: Do not press down on the screw whilst adjusting it, otherwise a false reading will be obtained.

11. When the carburettors are synchronised, open and close the throttle quickly to settle the linkage, and recheck the gauge readings, readjusting if necessary.

12. When the adjustment is complete, check the idle speed and adjust as required by turning the idle adjusting screw (see Section 2) until the idle speed listed in this Chapter's Specifications is obtained. Stop the engine.

13. Remove the vacuum gauges. Remove the adapter from No. 2 cylinder inlet manifold and fit the blanking screw.

14. Install the fuel tank (see Chapter 4).