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. Replacement is also called for if the advance portion cannot be calibrated to specifications. See "Ford Motor Co. Vacuum Advance & Retard Specifications" in IGNITION DISTRIBUTORS Section.