Those spark delay valves were only useful in one situation, installing them in the vacuum hose leading to the EGR valve diaphragm to slow down how soon the EGR valve would open, as on some engines the EGR opening at light throttle would cause a stumble. When they were used with the vacuum advance diaphragm tubing it slowed down how soon vacuum advance would be applied on off idle acceleration. The upside is for cars running low octane fuel it would pretty much eliminate any light acceleration pinging. The downside is the benefit of having vacuum advance being applied (better engine response at light throttle fuel economy) was muffled in an effort to further reduce NOx emissions. These are one way valves, so applied vacuum in one direction get slowed down, but in the other direction vacuum flows immediately (for vacuum release mode).
Back "in the day" when facing a complaint about poor low end acceleration and/or poor fuel economy with in town driving, I knew of "some folks" who would "clean out the valve restrictions with a small drill bit - heh heh... And, I also knew of folks who would install them in the vacuum line that would sent vacuum to the EGR Valve actuating diaphragm. In both cases the results were quite positive. Names are being suppressed to protect the guilty parties. heh heh... I will say, one of the folks that would install these vacuum delay valves in the EGR vacuum hose was a Ford factory trainer (now deceased) who said at times it is what it took to get a car to become more drivable in city traffic. He was my favorite Ford instructor, ever. I not only admired him for his no nonsensical diagnostic and repair approach, but he had Parkinsons and his tremor was quite pronounced. He refused to let his disease keep him from sharing his knowledge. I really enjoyed going to factory training whenever he was the instructor. RIP, Jim...
