[awbrown]

There have been other threads with this question , I searched my old threads but must have deleted it .. Most chevys will run best with manifold vacuum, the reason being is a lean mixture burns slower and needs more lead , and a rich mixture burns faster needing less ... timing , on chevys is always set with vacuum line off the distributor and plugged.. some of the time I ad adavance 2 degrees at a time til I it pings or detonates under load and then back it up 2 or 3 degrees and leave it ... you can limit the amount of vacuum advance it has with new can that is adjustable if you get a little rattle as you tip the throttle in ,or change the power valve / spring to richen it up depending on what carb you have ...