(1) Unscrew the fuel-hose assembly from the fuel-valve body only if this is necessary for maintenance. (2) Remove spring retainer and plug from end of fuel-valve body and remove valve spring. [Illustration: Fig 50. Valve needle, yoke block, and lock nut ready for installation in fuel-valve body.] (3) Unscrew diaphragm cap and pull out washer, support, and valve-diaphragm assembly. To prevent loss of valve-needle adjustment (Fig 54), do not disturb position of yoke block by turning the needle. [Illustration: Fig 51. Placing diaphragm assembly in position in fuel-valve body.] [Illustration: Fig 52. Installing parts in fuel-valve body.] (4) Slide the valve needle out of barrel; the yoke block and the lock nut may then be unscrewed from the valve needle, but adjustment (see _d_ below) will be necessary when reinstalling. _c. Installation of barrel and valve-body assembly._ (1) To install valve needle, screw the yoke block and lock nut on the needle (Fig 50). Insert needle in valve body and barrel. (2) Insert valve-diaphragm assembly into valve body (Fig 51), making sure that the yoke slips into the flat notches of yoke block. [Illustration: Fig 53. Installing spring retainer in fuel-valve body.] (3) Slip the diaphragm support, washer, and cap over the yoke shaft. (Fig 52) Screw on the diaphragm cap by hand. Do not use a wrench. Install valve grip. (Par 74 _c_) (4) Place valve spring over end of needle and install spring retainer. (Fig 53) Apply wrench very lightly to tighten spring retainer. (5) Adjust needle (see _d_ below), and screw plug into the spring retainer. (6) If hose has been removed, apply anti-seize compound lightly to the threads. Screw hose into fuel-valve body. Wrench should be applied very lightly to tighten. _d. Adjustment of valve needle._ Needle is adjusted after installation of parts in barrel and valve assembly. Use care when resetting needle, as smooth operation of the weapon depends on accurate adjustment. (1) Remove ignition shield (Par 18) and plug from gun. (2) Use the valve-adjusting wrench (Fig 8) to hold the lock nut and apply a cabinet (narrow-bladed) screw driver (Fig 8) in the end of the needle. Turn needle until it makes a snug fit in the nozzle opening. (3) Compress the valve lever and grip safety. The needle should draw back into the nozzle with the tip of the needle at the smallest diameter opening in the nozzle. (Fig 54) (4) When the needle has been correctly adjusted, as in (3) above, tighten the lock nut with the valve-adjusting wrench, keeping the needle from turning with the screw driver. This will lock the adjustment. Screw plug into the spring retainer. (5) Replace ignition shield. (Par 18) _e. Maintenance of barrel and valve body._