Background:

440 with stealth heads and forget pistons. 11:1 CR and 170 psi cranking compression with XE274 cam. Topped with edelbrock dual quad intake. Car is a 70 charger, auto, 3.23 and 30" tires. Initial timing is 10 deg, total 30, no vacuum advance. Car run on european 95 octane=91 us ?
Plugs look good, exhaust smells terrible rich.

Problem:
With above configuration car drives fine but exhaust burns eyes and advancing timing more than 10/30 (init/total) we get pinging while the rpms rise and combustion gets definitely better. We tried drilling butterflies but this barely helped. Controlled vacuum leak helps alot - rpms rise.

I advised him to play with different timing curves (we bought set of distributor springs) but it seems to have no effect. Leaning the idle circut (screws) has no effect - engine still runs (I guess butterflies are open and expose main circuit).

Any ideas how to tackle this problem?