GMC 4000 Series Service Manual page 339

Sec. 6M
Page 328
FUEL SYSTEM— GASOLINE ENGINES
ROCHESTER CARBURETOR TROUBLESHOOTING CHART (MODEL "M ")
C O M P L A IN T
C D
£ O
o o
eu a .
oo 1 =
t=
o
r o
Ll_
o
C D C D ca
t= o
T O
a .
C D
a_ C D a .
to /) T3
o «j
o
ra
C D O
JZ = £ =
o
C D to o 1 —
X3
■ a
sz
C D o
"O
o = 3 O
£
o aj
ca
o
u 3
o
cr LU _L <E O O
1 CJ CO
L i - — X
★ 1 ★
★
★
1
2 2 4
3 3
★ ★
1 ★
★
★ ★
★
1 ★ 1
★
2
★
3 2
4
★
5
★
2
6
1 1 ★
2a 3
2b 2 4 2
★
1
4 3 4
★
1
3 3
★ ★
3
★ ★ ★
★
3
★
4
★ ★ ★
★ ★
4
★ ★ ★ ★
★ ★ ★ ★ ★
2
★ ★
7
★ ★ ★
2
★
3
★
★ ★ ★ ★
★
★ 8 ★ ★
1 9 4
1
1
GMC OVE R HA UL MANUAL
Locate the complaint by reading across the top of the complaint columns, then find Step 1. If Step 1
does not remedy the complaint, move to Step 2 in that column. T a ke Steps 3, 4, 5, etc., in order
until you have located the trouble.
★ Indicates other possible trouble points.
C H E C K P O IN T S
ID LE A D JU ST M EN T
FLO A T A D JU ST M EN T
PUMP A D JU STM EN T
ID L E V EN T A D JU ST M EN T
CHO KE A D JU ST M EN T
CHOKE ROD A D JU STM EN T
UNLOADER A D JU ST M EN T (4M V)
F A S T ID LE A D JU ST M EN T
SECO N DARY LO CKO U T AD J.
T H R O T TLE RETURN CHECK
POWER PISTO N
M ETER IN G ROD
M ETER IN G J E T S
N EED LE & S E A T
FLO A T
ID LE N EED LES
T H R O T TLE V A LV ES
G A S K E T S
ID LE PA SS A G ES
CHOKE VACUUM PA SSA G E
PUMP PLUNGER
PUMP IN L E T CH EC K B A L L
★ P UMP DISCH A RG E CHECK
CHOKE V A LV E
D RIVER
HOT ID LE CO M PEN SATO R
Correct speed and m ixture
Use correct gauge
Use correct dim ension, throttle valves closed
Dirt, wear, sticking o p en; must be closed except at idle
Set to latest specification
Use correct gauge, fast idle screw on 2nd step of cam, next to high step
Use correct gauge, throttle valves wide o p en; check to see that throttle
linkage allow s wide open position on vehicle
Set with warm engine, use tachometer, set to information specification
Proper clearance so cam is free to move with throttle valves closed
Proper clearance with throttle lever, vacuum leaks
Dirty, distorted, sticking, incorrect part
Dirty, sticking, incorrect part
Loose, plugged, incorrect part
Worn, damaged, dirty, incorrect part
Bent, leaky
Worn, damaged
Sticking open or closed, damaged, not aligned properly
Im proper seal, hard or brittle m aterial, loose screw s
Dirty or plugged
Plugged or vacuum leaks
Hard or worn seal, distorted spring, stuck vent ball check
Out-of-round, damaged seat, stuck
Out-of-round, damaged seat, stuck, distorted spring
Dirty, damaged, sticking
Driving habits, correct procedures
Dirty, damaged, sticking
W H A T TO L O O K F O R