GMC 4000 Series Service Manual page 343

Sec. 6M
Page 332
FUEL SYSTEM— GASOLINE ENGINES
BENDIX-STROMBERG CARBURETOR TROUBLESHOOTING CHART
COMPLAINT
1
★ ★
3
3 ★ 2 3
1 ★
★ ★
1
2
1 1 52
2 2 4 1 ★
4 3 1 4 ★
1 ★ ★ 5
★ ★ 5 4 3 ★
2
★ ★
3
4 ★ ★ ★ ★ ★
4
★ ★ ★ ★ ★ ★ ★
2
★ ★ ★ ★
★
★
2
★
3
★
★ 4
★
★
★
NOTE: If the above complaints are persistent, check the governor diaphragm
assembly for possible engine oil leakage. Engine oil could travel through the car­
buretor governor and throttle body and contaminate the air-fuel mixture. Depletion
of engine oil supply may occur if the diaphragm is punctured.
G M C S E R V I C E M A N U A L
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. Take
Steps 3, 4, 5, etc., in order until you have located the trouble.
★ Indicate other possible trouble points.
CHECK POINTS
★1 ★ Idle Adjustm ent
3 2
Float A djustm ent
★ Pump Adjustm ent
1
Idle Vent Adjustm ent
★ Choke Adjustm ent
★ Fast Idle Adjustm ent
2 Throttle Return Check
Power Piston
Power Valve
Metering Jets
5 3 Needle and Seat
Venturi Cluster
★ ★ Float
★ Idle Needles
Throttle Valves
4 ★ Gaskets
★ ★ Idle Passages
Power Piston Vac. Pas. Plugged or vacuum leaks
Pump Shaft Seal
Pump Plunger
Pump Inlet Check Ball
★ Pump Discharge Check
★
3 ★ ★ Choke Valve
WHAT TO LOOK FOR
Correct speed and mixture
Use gauge and set to specifications
Use correct dimension, throttle valves closed
Dirt, w ear, sticking open; must be closed except at idle
Use correct gauge, fast idle screw on 2nd step of cam, next to high step
Set with warm engine, use tachometer, set to information specification
Proper clearance with throttle lever,
Bent or sticking, distorted spring
Dirty, sticking, loose, incorrect part
Loose, plugged, incorrect part
Worn, damaged, dirty, loose or incorrect part
Dirty, loose screw s, incorrect part
Bent, leaky, distorted float arm s
Worn, damaged
Sticking open or closed, damaged, not aligned properly
Improper seal, hard or brittle m aterial, loose screw s
Dirty or Plugged
Crack or loose fit on plunger shaft
Hard or worn leather, distorted spring, stuck vent ball check
Out-of-round, damaged seat, stuck
Out-of-round, damaged seat, stuck, distorted spring
Dirty, damaged, sticking