The key word is that you disconected the EGR valve , and yes most cars of that time will ping when you do , the reason is the exhaust gas does slow down the burn when the EGR valve is open , but now you have a timing to load problem , you can mask the problem with a few tricks and get rid of the ping , learned this when I worked at a ford stealership back in the 70s when al this emissions crap was being piled on the cars with miles of vacume lines and tees to tie them into a holy mess , the first you can try is to remove the line from the distribtor and find a allen wrench (or hex key) that just fits in to vacume advance can , you may have to try a few to find the one that fits , there is a screw inside the adjust the spring inside , from memory I would try one complete turn counter clockwise , mark it just in case youmay have to go the other way , no more than two turns max form your starting point , if that gets rid of the ping great , but if you still have just a trace the next thing you will have to rejet the carb , the bad news is no one supports the carb anymore , so its almost imposable , the only other option is to swap the carb with a 74 to 76 year carb , they ran a tad richer than the one you have now , that also will cover up the ping and give you a few more HP , why , well the newer 78 up carbs had less CFM than the older ones , hope this helps you , I got rid of my ping / fuel problem when I went to EFI , later Blaine