Vacuum Retard
Readjust engine idle speed to 550-600 RPM. Using a timing light, observe timing. Remove plug from manifold vacuum line and connect line to inner diaphragm. Timing should retard immediately. Replace dual diaphragm unit if either of the diaphragms are leaking or if the retard portion is out of calibration. The advance (outer) diaphragm on some models is adjustable. If vacuum advance is working okay but not to specifications, disconnect advance hose and adjust using an Allen wrench through vacuum nipple opening. See appropriate article in DISTRIBUTORS & IGNITION SYSTEMS section for specifications.