Slant-6 idle problems, need advise.....

My '69 Dart 225 w/ Holley 1920 never idled right until about the 4th carb I put on it. This was thru several head jobs, an intake manifold swap, and even a new long block. It was the carb all along. You can find other horror stories about badly rebuilt carbs on www.slantsix.org. It always idled lean, which causes stumbling and missing. Rich usually runs smooth until it dies or pours black smoke out the exhaust. One way to tell is that it idled best w/ the max spark advance I could give it, >30 deg, though the factory spec'ed more like 10 deg advance. I checked that my damper marks were correct w/ a dial indicator on the piston, thru the sparkplug hole. Good luck.

The other thing that drove me nuts was the choke pull-off diaphragm at the top of the carb. Once older and smarter, I learned that the choke plate should be closed when cold. Once the engine fires, the choke pull-off gets vacuum and pops the choke plate open slightly (to drill size shown in the manual). The problem is the diagphram rubber fails, especially when hit with carb cleaner. Check w/ a vacuum pump. You can buy just the pull-off. Carbs are quirky beasts.