Idle adjustment and CO
1. See specifications for idle speed of various models. Of particular note is the difference in idle speed with a 28x36 carburetor installed on the engine. Before making any adjustments, measure the idle speed. To do this, use the data of the tachometer and a device for measuring CO.
2. The air damper must be fully open.
3. Set the correct ignition timing.
4. Determine valve clearances.
5. Connect the tachometer and CO meter according to the manufacturer's instructions.
6. Install the air filter to the carburetor.
7. Warm up the engine until the thermostat opens. For this purpose, you can also drive a short distance.
8. Determine the engine idling speed using a tachometer and compare with the prescribed value.
9. Determine the CO content. The value must correspond to 1.5±0.5%, regardless of the type of carburettor. The idle mixture adjustment screw is closed with a plastic plug. This screw is used to set the CO content and the plug must always be changed if the screw has been opened for adjustment. Under normal conditions, it is sufficient to adjust the idle speed with a special screw.
Idle adjustment
10. Turn the throttle adjustment screw until the regulated idle speed is established. Increase the speed several times and let the engine idle.
11. Turn the screw until the maximum idle speed is reached.
12. Repeat both adjustments until the adjusted idle speed is held by the screw.
13. To lean the working mixture, screw in the adjusting screw until the engine reaches a shaft speed of 20-25 rpm. The final adjustment is always made by tightening or loosening another screw.
14. Install the CO meter according to the manufacturer's instructions. In case the value is not 1.5±0.5%, turn the screw accordingly.
15. Once again determine the engine idling speed using a tachometer and measure the CO content. If the adjustment is made in accordance with the standards, install a new seal on the screw.
Float installation
16. Place the carburettor cap down so that the weight of the float is sufficient to close the needle valve without pressing the sphere in the seat.
17. Measure the float travel between seal and float and, if necessary, change the travel by 7 mm by bending the float lever so that it does not interfere with the tongue.
18. Carefully move the float outward to check for extra travel. It should be 8 mm, i.e. the amount should be only 15 mm. Bend the tab when finished adjusting.
Throttle opening
19. Fully close the choke valves and make sure the screw is against the top lug of the starter cover. To control the throttle valve clearance, insert a flexible rod with a diameter of 0.8 mm between the throttle valve of the first chamber and the carburetor hole. The gap can be adjusted with a screw.