Testing Vacuum; Troubleshooting - Arctic Cat Sno Pro 120 Service Manual

TESTING VACUUM

 NOTE: Make sure adequate fuel is in the carburetor
for this test.
1. Connect Vacuum Test Pump directly to the fuel
pump inlet fitting.

Troubleshooting

Problem: Carburetor Too Rich (0-1/4 Opening)
Condition
1. Choke plunger will not seat
2. Pilot air screw too far in
3. Pilot air passage obstructed - damaged
4. Float/inlet needle obstructed - damaged - adjusted incorrectly
5. Pilot jet loose
Problem: Carburetor Too Rich (1/4-3/4 Opening)
Condition
1. Pilot air screw too far in
2. Needle jet needle worn - adjusted incorrectly - incorrect
3. Pilot air passage obstructed - damaged
4. Pilot jet loose
5. Float/inlet needle obstructed - damaged - adjusted incorrectly
6. Main jet loose - too large
7. Primary air passage obstructed
Problem: Carburetor Too Rich (3/4-WOT Opening)
Condition
1. Main jet loose - too large
2. Float/inlet needle obstructed - damaged - adjusted incorrectly
3. Needle jet needle worn - adjusted incorrectly - incorrect
Problem: Carburetor Too Lean (0-1/4 Opening)
Condition
1. Choke plunger remains seated
2. Pilot air screw too far out - damaged
3. Piston valve sticks open - damaged - worn
4. Pilot jet - outlet obstructed
5. Float/inlet needle obstructed - damaged - adjusted incorrectly
Problem: Carburetor Too Lean (1/4-3/4 Opening)
Condition
1. Pilot air screw too far out - damaged
2. Needle jet obstructed
3. Pilot jet - outlet - main jet obstructed
4. Float/inlet needle obstructed - damaged - adjusted incorrectly
5. Jet needle E-clip position incorrect
Problem: Carburetor Too Lean (3/4-WOT Opening)
Condition
1. Main jet obstructed - too small
2. Float/inlet needle obstructed - damaged - adjusted incorrectly
3. Needle jet needle obstructed
Problem: General Fuel System (Engine Cuts Out at High RPM)
Condition
1. Fuel delivery inadequate
2. In-line fuel filter obstructed - damaged
3. Gasoline contaminated
4. Gas-tank vent - hose obstructed
Problem: General Fuel System (One Cylinder Runs Lean)
Condition
1. Carburetor-to-cylinder air leak
2. Carburetors not aligned vertically
3. Primary compression (crankcase) low
4. Carburetors not synchronized
4-12
2. With snowmobile on a safety stand, start the engine
and accelerate to 2000-3000 RPM for a period of 30
seconds. Note maximum reading of gauge. Reading
must be 7-10 in.-hg.
3. Stop engine. Connect fuel hose. Turn the shut-off
valve to the OPEN position.
Remedy
1. Adjust - service - replace choke cable - plunger assembly
2. Adjust pilot air screw
3. Remove obstruction - replace pilot air screw - carburetor
4. Remove obstruction - replace inlet needle - float - adjust float tab
5. Tighten pilot jet
Remedy
1. Adjust pilot air screw
2. Replace needle jet - replace - adjust jet needle E-clip
3. Remove obstruction - replace pilot air screw - carburetor
4. Tighten pilot jet
5. Remove obstruction - replace inlet needle - float - adjust float tab
6. Tighten - replace main jet
7. Remove obstruction
Remedy
1. Tighten - replace with smaller main jet
2. Remove obstruction - replace inlet needle - float - adjust float tab
3. Replace needle jet - replace - adjust jet needle E-clip
Remedy
1. Adjust - service choke cable - plunger assembly
2. Adjust - replace pilot air screw
3. Service - replace piston valve - throttle cable - spring
4. Remove obstruction
5. Remove obstruction - replace inlet needle - float - adjust float tab
Remedy
1. Adjust - replace pilot air screw
2. Remove obstruction
3. Remove obstruction
4. Remove obstruction - replace inlet needle - float - adjust float tab
5. Adjust E-clip
Remedy
1. Remove obstruction - replace with larger main jet
2. Remove obstruction - replace inlet needle - float - adjust float tab
3. Remove obstruction
Remedy
1. Repair - replace fuel pump - impulse hose
2. Remove obstruction - replace in-line fuel filter
3. Replace gasoline - de-ice - clean carburetors
4. Remove obstruction - replace vent - hose
Remedy
1. Repair/replace gaskets/flanges - service intake ports - tighten
clamps
2. Align carburetors vertically
3. Troubleshoot engine
4. Synchronize carburetors