CAUTION: An idle speed that is too low results in gearbox  damage, and if an idle speed is too high, the engine is harder  to start. Start the engine and verify the idle speed. If the idle  speed is too high or too low, adjust accordingly with idle speed  adjustment screw (2). Check the operational idle mixture of  the engine. If necessary, adjust with the idle mixture screw (6).  Mechanical synchronization should have already been  accomplished. The two carburetors are adjusted to equal  flow rate at idling by use of a suitable flow meter or vacuum  gauges (1). There are two possible methods to connect test equipment.  One option is to remove hex screw (6) M6 x 6 from the  intake manifold (7) and connect the vacuum gauge(s).  [Figure 11-26  and  Figure 11- 29]  Remove the compensating  tube (2) with attached hoses (12) (connection between intake  manifolds) and plug the connections in the intake manifolds.  The other hook up option is to remove the compensating tube  hose (2) from the push-on connection (5) after removing the  tension clamp (4). Using the push-on connection (5), install  a flexible rubber hose (8) leading to the vacuum gauge (1),  using the balance tube (4). Install the other flexible rubber  hose leading to the vacuum gauge.  [Figure 11-29]  Before  proceeding any further, secure the aircraft on the ground  using wheel chocks and ropes. WARNING: Secure and observe the propeller zone during  engine operation. Start the engine, verify the idle speed, and make any  necessary corrections. If a setting correction of more than ½  turn is required, repeat mechanical synchronization to prevent  too high a load on the idle stops. If the idle speed is too high,  the maximum the idle screw can be unscrewed is a complete  turn. If no satisfactory result can be achieved, inspect the idle  jets for contamination and clean if necessary.  Caution: Also check for translucent, jelly-like contamination.  Inspect for free flow.  Once the proper idling speed has been established, it is  necessary to check the operating range above the idle speed.  First, establish that the engine is developing full takeoff  performance or takeoff rpm when selected in the flightdeck.  Then, the setting of the operating range (idle to full throttle)  can be checked or adjusted. 0 3 1 2 4 5 6 7 bar 01 0 3 1 2 4 5 6 7 bar 01 1 2 8 4 4 5 CODE 1 2 4 5 Flow meter/vacuum gauge Compensating tube hose Tension clamp Push-on connection Flexible rubber hose 8 Figure 11-29. Gauges attached to the engine. Pneumatic Synchronization 11-19