Can't advance timing?

Whoa...50 degrees of initial timing????
You are aware that these engines do not like, want or need that much, right? A stock 318 needs maybe 7 degrees BTDC at idle with a total centrifugal advance of 33-35 at around 2800 rpms. The vacuum advance adds even more than that but will be reduced at WOT and even at part throttle somewhat.
Are you checking the timing with the vacuum advance hose connected to a manifold vacuum port?