TM 10-3930-653-14&P (2) REPLACING FUEL FILTER Check for a contaminated element, and water deposit. Fig.  4-12.  Fuel Strainer This  engine  uses  a  cartridge  type  strainer,  so  if   a malfunction is detected.  replace filter element #6 In the above figure. (3) CHECKING  THROTTLE  VALVE  AND  CHOKE VALVE (1) Check  throttle  valve  shaft  for  wear.    Make  sure that   there   is   no   play   of   throttle   lever   by   moving   it. Replace throttle valve shaft if it is worn excessively. (2) Check opening and closing of  throttle  valve  and choke valve.  Choke valve should close fully when choke lever is pulled all the way.  Choke valve should open fully when   choke   lever   is   released.      If   any   malfunction   is found, adjust wire. (3) Check    choke    interlocking    mechanism.        (For details, refer to Section 5.) (4) ADJUSTING CARBURETOR-IDLE RPM MIXTURE RATIO The idle adjustment is  made  by  the  throttle  adjusting screw  and  the  idle  adjusting  screw  after  the  engine  is warmed up. 1.  Idle adjusting screw 2.  Throttle adjusting screw Fig.  4-13.  Idling Adjustment (1) Check if engine idle speed is at specified value. (2) Using    a    suitable    screwdriver.        turn    out    idle adjusting screw approximately two or three turns. starting from fully closed position Turn In throttle adjusting screw two or three turns and start engine. (3) Turn   out   throttle   adjusting   screw   gently   until specified engine Idle speed is approximately obtained. (4) Turn  in  or  out  Idle  adjusting  screw  until  engine runs smoothly at the highest speed. (5) out throttle adjusting screw until specified engine speed is obtained. (6) Readjust  idle  adjusting  screw  until  engine  runs smoothly at the highest speed (with the highest vacuum reading). (7) Then  throttle  adjusting  screw  must  be  adjusted so that engine speed is 20 rpm faster than specified. (8) Finally, turn In idle adjusting screw until specified engine speed is attained. WARNING Carbon   monoxide   gas   is   a   colorless,   odorless, poisonous,  deadly  gas  produced  by  incomplete combustion of any carbon containing material.  It occurs   in   the   exhaust   fumes   of   fuel   burning internal combustion engines, and becomes dangerously   concentrated   under   conditions    of inadequate ventilation. Note: a.    Items  (7)  and  (8):    Best  method  to  reduce  carbon monoxide in exhaust emission. b.  Do not attempt to screw down the idle adjusting screw completely.    It  may  result  in  damaging  the  tip  which will tend to cause malfunctions. 4 - 13