Test 20 - Carburetor Bowl Vent System Check

Remove bowl vent hose from carburetor and canister. Blow lightly into hose. Air should flow through hose. If air flows through hose, proceed to step 2). If air does not flow through hose, clear hose or replace bowl vent valve. Look for liquid in hose near canister. If liquid is found, check routing of hose.
NOTE: If vehicle has been updated using Technical Service Bulletin 18-31-85, the bowl vent hose will have a thermo valve in it. If ambient temperature is below approximately 50°F (10°C) the thermo valve will close.
With bowl vent hose removed from carburetor and canister, start engine and blow lightly into hose. Air should not flow through hose. If air flows through hose, check for air pressure in hose from air switch relief valve. Repair as required. If okay, replace bowl vent valve.
If air does not flow through hose, disconnect air duct from air cleaner snorkel. Disconnect vacuum supply hose to heated air intake system air temperature sensor. Try to apply vacuum to air temp sensor with a vacuum source. Vacuum should not hold and heated air door should be open. If okay, proceed to TEST 21 . If vacuum holds, replace sensor. If heated air door is not open, repair or replace as required.