TRUCK SERVICE MANUAL
Fuel Filter Restriction
1 Fuel filter restriction can be checked using ST434
Vacuum Gauge. Fig. 534.
2. Connect gauge using the special adapter furnished in
ST434.
3. If restriction reads 8 inch vacuum while engine is
running at full speed and load, filter must be changed or other
sources of restriction remedied. Sight glass gauge, (ST998),
will show air bubbles with air entrainment and possible gasket
or other leaks.
Fig. 535 F5181. Sealing fuel pump
b. Wire the spring pack as in Step 2 except before
sealing, run wire through capscrew hole in lower drive cover.
c. Twist wire and seal as in Step 2.
4. Throttle Adjusting Setscrew Seal.
a. Install acorn nuts on setscrews.
b. Insert wire through drilled hole in acorn nuts.
c. Twist wire down to throttle shaft.
Fig. 534. F51 80. Checking fuel restriction
d. Place wire behind throttle lever and straddle throttle
shaft.
4. If air bubbles are persistent and the engine is over
e. Twist wire and insert through lower hole in throttle
400 brake horsepower, check the float valve assembly in the
shaft cover.
float tank (if so equipped). The gear pump may be pumping
f. Bend twisted wire into seal and press on top half of
more fuel than the float valve will allow to pass into the float
seal.
tank. A new interchangeable float valve is available with
sufficient capacity to meet this requirement.
5. An optional spring pack
cover,
without
idle
adjustment .access hole, is available.
Seal Fuel Pump
a. After pump is calibrated, remove the cover with
1. To prevent unauthorized adjustments of the fuel
access hole and install plain cover.
pump after final adjustments are made, seal the spring pack.
b. Install lockwire through capscrew hole and secure
housing lower capscrews and the rear throttle screw or throttle
seal as before.
cover and spring pack cover plug. Fig. 535.
6. To further protect fuel pumps from tampering; a new
2. Spring Pack Housing Seal.
countersink drill (ST1175), a twistoff countersink capscrew
(204925) and a countersink lockwasher (204926) is available.
a. Install bottom capscrew with drilled hole in head.
Install plug with drilled hole into spring pack housing.
a. Remove one or more capscrews, lockwashers and
b. Insert seal wire through capscrew and plug.
flatwas'hers from the front cover and/or spring pack cover.
c. Twist the seal wire ends together until connection is
secure and wire is tight.
b. Use st-1175 countersink drill to counterbore the cover
d. Bent twisted wire into seal and press on top half of
so the twist-off capscrew will be flush with the surface, Fig 5-
seal.
3-5.
3. Drive Cover Seal.
c. Apply Loctite to capscrew counterbore surface and
install capscrews and countersunk lockwashers in covers.
a. Use a longer wire to reach a lower capscrew on the
drive cover.
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