Incorrect Reading On Hard Acceleration Above 15 Mph

If voltage is noted but not vacuum, replace control switch. If neither vacuum nor voltage were noted, check for ported vacuum at 4500 RPM at EGR control solenoid valve A inlet.
If vacuum is found, replace EGR control solenoid valve A. If no vacuum, check hose routing, clean carburetor port and retest.

Fig 1: EGR Vacuum Bleed Location
Courtesy of AMERICAN HONDA MOTOR CO., INC.