Carburettor idle speed and mixture - adjustment

Fuel system / Carburettor idle speed and mixture - adjustment

1 All carburettors have their mixture adjustment set in production. The screw is fitted with a tamperproof cap.

2 Under normal circumstances, only the idle speed screw need be adjusted to set the engine idle speed to the specified level.

3 Before attempting to adjust the idle speed or mixture, it is important to have the ignition and valve clearances correctly set and the engine at normal operating temperature with the air cleaner fitted.

4 Where the mixture must be adjusted, prise out the tamperproof plug and turn the mixture screw in to weaken or out to enrich the mixture until the engine runs smoothly without any tendency to “hunt”.

5 Ideally an exhaust gas analyser should be used to make sure that the CO level is within the specified range.

6 Once the mixture has been correctly set, re-adjust the idle speed screw.