I have a 72 pontiac 400 that pings and knocks upon acceleration. There is no timing tab for me to correctly time it, however I have hooked a timing light up to it and turned the HEI distributor so that the mark on the balancer is pointed in the general direction of where a timing tab should be. Also, I am getting a steady vacuum reading of "17". Should I install a timing tab, if so what degrees should it be set at? Should I try premium gas?
It should be 10 degrees for a stick and 12 for an automatic. But if this has a cam that is higher than what cmea stock, throw that stuff out thewindow. Disconnect the vacuum line andplug it before setting timing. If it still pings you'll have to back it off until it stops. If that doesn't work try premium or a GOOD additive. By allmeans put anew timing tab back onso you'llknow what you have.