I just finished installing my re-build 289, Edelbrock Manifold and 4B carb. Idles great but stalls under load when I put it in gear (C4-Automatic). I don't have any exhaust installed yet, only the stock manifolds. Can no back pressure be causing this problem? Timing doesn't seem to help (tried a lot of settings from 6-12 degrees BTDC and disconnected the vacumm advance. Don't believe I have any vacumm leaks. HELP!