Chevrolet DB90 Series, Service Manual

Page: 106 / 242

Sec. 6M-100
FUEL SY STEM —G A S O L IN E EN GIN ES
the carburetor throttle le v e r r e su lts in the idle
speed given e a r lie r in Step 1.
2. Rotate id le m ixture sc r e w s counterclock­
w ise until tang on each p la stic cap contacts main
body of carburetor a s shown in View B , figu re 2.
3. R eset the idle speed a s d irected in Step 1.
4. Turn "in" id le m ixture sc r e w s equally by
rotating clock w ise to LEAN m ixture until the fo l­
lowing idle sp eed s a re reached:
Engine Idle Speed
401M, 478M . .
4 7 8 S N ...............
637-V8 ............
Figure 6 —Checking Float Level
CARBURETOR ADJUSTMENT
1. Engine idle speed should be:
Engine Idle Sneed
401M, 478M . . .
4 7 8 S N ..................
6 3 7 - V 8 ...............
If n ec e ssa r y to adjust id le speed perform the
following:
a. R eferring to figure 5, p lace a %-inch open
end w rench on diaphragm extension of vacuum idle
stop to prevent its rotation w hile adjusting plunger.
CAUTIO N : UNDER NO CONDITIONS
SHOULD TH E DIAPHRAGM EXTEN SIO N
B E A LLO W ED TO R O T A T E OR IN TER N ­
A L DAMAGE W IL L R E S U L T TO VACUUM
ID L E STOP UNIT.
b. Adjust the plunger with a 3 /8 -in c h open
w rench until the fa ce of the plunger hex contacting
FLO AT LEVEL ADJUSTM EN T
1. R em ove air clean er and disconnect choke
and a c c e le ra to r linkage and fuel lin e from carbur­
etor. D iscon n ect fast idle link and a ccelera to r
pump rod.
2. R em ove carb u retor-to-m an ifold retaining
b olts or nuts, then rem ove earburetor from engine.
3. R eferring to View A, figure 2, rem ove
th ree short sc r e w s , four long s c r e w s, and sp ecia l
s c r e w . Separate air horn and throttle body from
main body of carburetor. Carefully pour fuel from
float bowl.
4. Hold main body inverted as shown in figure
6. T his w ill allow w eight of float to hold needle in
the c lo se d position . U se float gauge (J-8824) to
check relationship of the float to top of the fuel
bowl a s shown. R efer to sp ecifica tio n s for proper
float le v e l adjustm ent. Setting i s c o rrect when the
edge of the gauge touches top of the rib on float.
5. U se tool (J-4395) to bend float le v e r next
to float to change the float settin g. U se bending
to o l a s illu str a ted in figu re 7.
Figure 7 —T yp ical Use o f Bending Tool to Set Float Level
CHEVROLET SERIES 70-90 HEAVY DUTY TRUCK SHOP MANUAL SUPPLEMENT