Carburetor Removal Carburetor Maintenance Rigging Carburetor Controls Installation of Carburetor Adjusting Idle Mixtures 2-30 Excessively rich or lean idle mixtures result in incomplete  combustion within the engine cylinder, with resultant  formation of carbon deposits on the spark plugs and  subsequent spark plug fouling. In addition, excessively rich  or lean idle mixtures make it necessary to taxi at high idle  When installing a carburetor that uses diaphragms for  controlling fuel flow, connect the fuel lines and fill the  carburetor with fuel. To do this, turn on the fuel boost pump  and move the mixture control from the idle cutoff position  to rich position. Continue the flow until oil-free fuel flows  Inspect the induction passages for the presence of any  foreign material before installing the carburetor. As soon  as the carburetor is placed in position on the engine, close  and lockwire the throttle valves in the closed position until  the remainder of the installation is completed. Place the  carburetor deck screen, when feasible, in position to further  eliminate the possibility of foreign objects entering the  induction system. Remove the protective cover from the carburetor mounting  flange on the engine. Place the carburetor mounting flange  gasket in position. On some engines, bleed passages are  incorporated in the mounting pad. The gasket must be  installed so that the bleed hole in the gasket is aligned with  the passage in the mounting flange. When installing carburetors or fuel metering equipment  incorporating manual-type mixture controls that do not have  marked positions, adjust the mixture control mechanism  to provide an equal amount of springback at both the rich  and lean ends of the control quadrant in the cockpit when  the mixture control on the carburetor or fuel metering  equipment is moved through the full range. Where mixture  controls with detents are used, rig the control mechanism  so that the designated positions on the control quadrant in  the aircraft agree with the corresponding positions on the  carburetor or fuel metering equipment. Controls should  move freely and smoothly without binding throughout  their total travel. In all cases, check the controls for proper  positioning in both the advance and retard positions. Correct  excess play or looseness of control linkage or cables. Safety  all controls properly to eliminate the possibility of loosening  from vibration during operation. Check the carburetor for proper lockwiring before installation  on an engine. Be sure that all shipping plugs have been  removed from the carburetor openings. Connect and adjust carburetor or fuel metering equipment  throttle controls so that full movement of the throttle is  obtained from corresponding full movement of the control  in the cockpit. In addition, check and adjust the throttle  control linkages so that springback on the throttle quadrant  in the aircraft is equal in both the full-open and full-closed  positions. Correct any excess play or looseness of control  linkage or cables. Controls should be checked so that they  go stop-to-stop on the carburetor. Check for complete and  full travel of each control. Before removing a carburetor, make sure the fuel shutoff (or  selector) valve is closed. Disconnect the throttle and mixture  control linkages, and lockwire the throttle valve in the closed  position. Disconnect the fuel inlet line and all vapor return,  gauge, and primer lines. If the same carburetor is to be re- installed, do not alter the rigging of the throttle and mixture  controls. Remove the airscoop or airscoop adapter. Remove  the air screens and gaskets from the carburetor. Remove  the nuts and washers securing the carburetor to the engine.  When removing a downdraft carburetor, use extreme care  to ensure that nothing is dropped into the engine. Remove  the carburetor. Immediately install a protective cover on the  carburetor mounting flange of the engine to prevent small  parts or foreign material from falling into the engine. When  there is danger of foreign material entering open fuel lines  during removal or installation of the carburetor, plug them  using the proper cover fittings. The removal procedures vary with both the type of  carburetor concerned and the type of engine on which it  is used. Always refer to the applicable manufacturer’s  technical instructions for a particular installation. Generally,  the procedures are much the same, regardless of the type  of carburetor concerned.  from the drain valve. This indicates that the preservative  oil has been flushed from the carburetor. Turn off the fuel  flow, plug the fuel inlet and vapor vent outlet, and then allow  the carburetor, filled with fuel, to stand for a minimum of  8 hours. This is necessary in order to soak the diaphragms  and render them pliable to the same degree as when the unit  was originally calibrated. Tighten the carburetor mounting  bolts to the value specified in the table of torque limits in the  applicable maintenance manual. Tighten and safety any other  nuts and bolts incidental to the installation of the carburetor  before connecting the throttle and mixture-control levers.  After the carburetor has been bolted to the engine, check the  throttle and mixture-control lever on the unit for freedom of  movement before connecting the control cables or linkage.  Check the vapor vent lines or return lines from the carburetor  to the aircraft fuel tank for restriction.