TM 5-4240-501-148P CARBURETION Automatic Choke 3. If the engine can be started, run for 2 or 3 minutes, at a normal operating speed.  Check to be sure fuel tank is 1/2 full of fuel.  Then, open the needle valve to  be  sure  the  mixture  can  be  made  too  rich.    Next close the needle valve to be sure the mixture can be made   too   lean.      Adjust   needle   valve   to   midpoint between too rich and too lean. Allow engine to run at idle speed for 3 to 5 minutes. Again,    close    needle    valve;    the    mixture    should become  so  lean  the  engine  will  stop.    If  the  engine continues to run at idle with the needle valve closed, a fuel leak is occurring at one of the following areas: Check items 2D, 2H, 2I, 2.J and 2K. If the choke valve does not react as stated in Steps 1, 2 and  3,  the  carburetor  will  have  to  be  disassembled  to determine the problem.  (See Repair Procedure below). The  following   list   is   given   to   aid   you   in   checking   the performance     of     the     Automatic     Choke     Carburetion System. 1.  Engine Appears to be Under-Choked A. Carburetor adjusted too lean B. Fuel    pipe    check    valve    inoperative    (Vacu-Jet only) C. Bent air cleaner stud D. Sticking choke shaft due to dirt, etc. E. Choke spring damaged or too short (See Repair Procedure) F. Diaphragm not preloaded (See Repair Procedure) 2.  Engine Appears to be Over-Choked A. Carburetor adjusted too rich B. Bent air cleaner stud C. Sticking choke shaft due to dirt, etc. D. Ruptured diaphragm E. Vacuum passage restricted F. Choke spring distorted, stretched, etc. G. Gasoline or oil in vacuum chamber H. Leak between link and diaphragm I. Diaphragm    folded    during    assembly,    causing vacuum leak J. Machined   surface   on   tank   top   not   flat   (See Repair Procedure) K. Needle valve seat loose REPAIR PROCEDURE Inspect  the  automatic  choke  for  freeness  of  operation. Any  sticking  problems  should  be  corrected,  as  proper choke  operation  depends  on  freedom  of  the  choke  to travel as dictated by engine vacuum. Repair procedures specific to the automatic choke are as follows: Remove the carburetor and fuel tank assembly from the engine.  The choke link cover may now be removed and the    choke    link    disconnected    from    the    choke    shaft. Disassemble   carburetor   from   tank   top,   using   care   to insure diaphragm is not damaged. CHECKING DIAPHRAGM AND SPRING The diaphragm is suitable for further use, provided it has not  developed  wear  spots  or  punctures.    (On  Pulsa-Jet models    check    to    insure    fuel    pump    valves    are    not damaged.) Also check choke spring length.  The Pulsa- Jet  spring  minimum  length  is  1-1/8"  -maximum  1-7/32" and    the    Vacu-Jet    spring    minimum    length    is    15/16" maximum  1".    NOTE  :  On  Model  110900  and  111900 choke   spring   minimum   length   is   15/16";   maximum   1- 3/8".  If spring length is shorter or longer than specified, replace diaphragm and spring. CHECKING TANK TOP The  machined  surface  on  the  top  of  the  fuel  tank  must be flat in order for the diaphragm to provide an adequate seal  between  the  carburetor  and  tank.    If  the  machined surface on the tank is not flat, it is possible for gasoline to  enter  the  vacuum  chamber  by  passing  between  the machined    surface    and    diaphragm.        Once    fuel    has entered  the  vacuum  chamber,  it  can  move  through  the vacuum  passage  and  into  the  carburetor.    The  flatness of the machined surface on the tank top can be checked by straight edge and feeler  gauge,  as  shown  in  Fig.  10. A   .002"   feeler   gauge   should   not   enter   between   the straight  edge  and  machined  surface,  when  checking  at the shaded areas depicted in the drawing.  Replace tank if  gauge  enters.    NOTE:  STRAIGHT  EDGE  MUST  BE ACCURATE. 5