CARBURETTOR SYNCHRONISATION AND IDLE ADJUSTMENT
Proper carburettor synchronisation and idle adjustment requires an exhaust gas CO meter, a rev-counter and a four-column mercury manometer.
Proceed as follows:
Disconnect the throttle control rod and lever (1).
Unscrew the idle speed screw (2) out of contact with lever extension (3).
Unscrew the screw (4) of the balance lever (5) until the throttles of both front and rear carburettors are fully closed. Check they are with light upward pressure on lever (1) While maintaining pressure on lever (1), tighten screw (4) until it contacts the tongue of lever (1), thus fully closing the throttles of both front and rear carburettors.
Tighten the screw (2) one more turn after it first contacts the extension (3) of lever (1).
Remove the anti-tamper seals from the mixture screw housing (6) and unscrew each screw five turns from the fully-closed position.
Check that the idle air bypass screws, to which anti-tamper paint has been applied, are completely closed- Remove the depression blanking plugs (8) and connect each barrel to the four-column mercury monometer using the screw-in adaptors.
Reconnect the Throttle operating rod to lever (1).
Start the engine and leave it running to attain normal operating temperature.
First ensure that any airlocks are removed from the mercury columns which will otherwise result in inaccurate readings.
Align the lower mercury column of the front carburettor with the lower one of the rear carburettor using balance screw (4).
Then, if necessary, adjust the levels of the other two cylinders to match those of the lowest pair using the bypass screws on these barrels With the No 1 cylinder blow-by pipe temporarily clamped shut, all readings should be brought to the same level. Unclamped for normal running, No 1 cylinder’s mercury level will always be lower than the other three cylinder levels.
Insert the CO tester probe and connect the rev counter.
Preferably only by using the pecial DeIl’Orto screwdriver, adjust the running of each cylinder by turning the mixture screw (6) to get the most even running with the engine idle speed at the correct level and holding the exhaust CO level well below 4,5%. Remember that by unscrewing these screws you increase the CO level and vice versa. The mixture screw of barrel (1) will need to be opened more than the others due to the effect of the blow by hole on that cylinder- Remove the vacuum adaptor plugs and refit the blanking plugs in their place.
Fit new anti-tamper seals on the mixture screw housings (6).
If all the above-mentioned equipment is not available, it is still possible to obtain the correct idle setting by simply resetting the idle speed screw (2) at the balance adjusting screw (4).