TM 10-3930-653-14&P Fig. 4-123.  Condition under Full Opening of Valve Fig. 4-124.  Condition under Total Closure of Valve (2) Force  to  close  the  valve  produced  by  the  pressure difference between both sides of it. This force acts more strongly when the throttle axle of    the    carburetor    is    wide    open    and    the    engine    is operating   at   high   speed.      The   rotation   axis   of   the governor  valve  is  shifted  from  the  center  of  the  valve  in such  a  direction  that  the  negative  pressure  suction  will tend   to   close   the   valve.      When   the   revolution   of   the engine increases with the throttle valve of the carburetor wide  open,  the  pressure  difference  between  both  sides of the governor valve increases with a resultant  increase in  the force which tends to close the valve. This  force  sharply  increases  when    the   governor valve  approaches  its  closed  position,  but  at  the  same time, the counteraction to open the valve exerted by the cam   and   cam   spring   also   rapidly   increases,   bringing about  a  balance  between  these  two  forces.    If  the  cam and  cam  spring  are  adjusted  improperly,  good    balance is   destroyed   and   causes   such   problems   as   overrun, engine    stall,    or    hunting:        ("Hunting"    means    sudden fluctuation of engine speed accompanied with vibration). Fig. 4-125. (3) Force to close the valve due to the stabilizer. This force is more strongly exerted when the throttle valve  of  the  carburetor  is  opened  comparatively  a  little, and  the  engine  is  rotating  at  a  high  speed.    When  the opening of the throttle valve of the carburetor is relatively small, the volume of air suction is small and the pressure difference   between   both   sides   of   the   governor   valve does   not   increase   in   spite   of   high   revolution   of   the engine,  disabling  the  valve  to  close.    The  stabilizer  is provided to compensate for this action. The smaller the opening of the  throttle  valve  of  the carburetor  and  the  higher  the  revolution  of  the  engine, the  larger  the  negative  pressure  suction  becomes  and the stronger the sucking force becomes on the stabilizer piston  Therefore,  the  force  of  the  piston  overcomes  the combined  force  of  the  cam  and  cam  spring  and  moves the  governor  valve  towards  the  closing  direction.    The stabilizer   piston,   at   the   same   time,   serves   to   prevent hunting,  because  it  always  pushes  the  valve  due  to  the force exerted by sucking action of negative pressure. 4-74