WEAK VALVE SPRINGS?

[GSW38]

MY 1938 SERIES 40 BUICK HAS A OCCASIONAL POP BACK THROUGH CARB.I INSTALLED A VACUME GAGE NEEDLE OSCILLATES QUICKLY BETWEEN 18 AND 20 IN OF VACUME AT IDLE.AS ENGINE RPM IS INCREASED OSCILLATIONS GET MORE VIOLENT BETWEEN 16 AND 22 IN.I SUSPECT WEAK VALVE SPRINGS. IS THEIR ANOTHER TEST I CAN DO TO CONFIRM THIS?

THANKS GEORGE

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