Emission System Servicing & Testing

CARBURETOR & DISTRIBUTOR
Other than making sure that the carburetor and distributor are functioning properly, make sure that the correct carburetor and distributor are used for the specific engine-transmission combination.




BYPASS VALVE
With transmission in neutral, accelerate engine and allow throttle to close rapidly. The valve is operating properly if no exhaust backfire occurs. Another check is to listen for air momentarily rushing through the bronze silencer immediately after throttle closure.




CHECK VALVE
To check valve for proper operation, disconnect air supply hose from pump at distribution manifold. With engine running, there should be no exhaust gas leakage at check valve.




DIVERTER VALVE
1. Start engine and allow to idle.
2. Check diverter vents. Little or no air should be felt flowing from vents.
3. Accelerate engine to 2000---3000 RPM and quickly close throttle. A strong flow of air should pass from diverter vents. If air does not flow or if backfire occurred, make sure that vacuum sensing line has vacuum and is not leaking. This valve diverts air pump output when 20 inches Hg or more is applied to vacuum sensing line or pump output exceeds 5 psi.
4. Slowly accelerate engine. Between 2500 and 3500 RPM, air should begin to flow from diverter valve vents.




AIR PUMP FUNCTIONAL TEST
To check for proper operation, disconnect air outlet hose at pump. With engine running, air discharge should be felt at the pump outlet opening. On early units, the pump output pressure is determined by the relief valve setting which is pre-set and not adjustable.

Pump Noisy Or Seized

The air pump is not completely noiseless. Under normal conditions, noise rises in pitch as engine speed increases. Also, allow a reasonable amount of time for a new pump to wear in before replacing it. Do not confuse air pump noise with other engine components.
1. Check belt tension, adjust as necessary.
2. If pump noise is still heard, remove belt to determine if pump is at fault. Check that pump is operative by turning pulley. A seized pump will not rotate and the noise can be caused by the belt slipping.
3. If pump is not seized, but it is determined that excessive pump noise is present, reinstall belt and proceed as follows:
a. Check to make sure all hoses are in good condition and properly connected.
b. With pump operating, check entire system for leaks in the hoses and around clamps. With engine idling, breaks in hoses can be located by feeling for air blowing through any holes.
c. Check for air leaks around clamps in the same manner or by using a soap and water solution.
d. Check that pump mounting brackets are not broken and that mounting bolts are tight.
e. Check relief valve (if used). Valve has failed if air escapes from the valve at engine idle speed.
f. A chirping or squeaking noise is most likely caused by the vane rubbing in the housing bore. This noise is most noticeable at low speed and is heard intermittently. Frequently vane chirp may be eliminated by allowing the vanes more break in time.
g. Bearing noise is noticeable at all speeds and makes a rolling sound. This noise does not necessarily indicate bearing failure. However, if bearing noise increases to an objectionable level at certain speeds, the pump may have to be replaced. Rear bearing failure can be distinguished as a continuous knocking sound. Such a sound requires pump replacement.

PUMP INOPERATIVE

If it has been determined that the air pump is not delivering air (check for lack of air flow by disconnecting an air hose and idling engine), proceed as follows:
1. Check belt tension. Note that excessive belt tension can damage the pump. When setting belt tension to specifications, do not pry on pump housing.
2. Check entire system for leaks in the hoses and around the clamps. As the pump is operating with the engine idling, breaks in hoses can be located by feeling for air blowing through any holes. Inspect the entire length of hose.
3. Check for air leaks around clamps in the same manner as above or by using a soap and water solution.
4. If the above steps do not solve the cause of no air delivery, the pump should be replaced.