Chevy SB vacuum advance
I have a '72 Chevy truck, stock. I recently had it worked on and it now runs poorly. It pings under heavy accel. It feels like the advance curve is messed up. Visual inspection has me confused. The vacuum advance is connected to the service that provides no advance at idle (i.e. when the butterfly is closed). I always thought that you would have vacuum on the distributor except when engine was under full load. Should the vacuum advance be connected directly to the intake manifold? If someone could point me to any good books or web pages on engine timing vs RPM vs load I would be thankful.