1966 Plymouth Valiant /6 & Holley 1945 carb can only get to idle at 1250rpm. How to get a lower idle without dying?

you replace this vacuum cap, it looks a little sus.

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what's the chrome capped breather attached to?

lets see a wide angle of what you got cookin. might be something obvious that's just hooked up wrong. pull the air cleaner so we can get a good look at the carb too.