My 1968 289 is running like total crap in idle, shaking, low rpm, struggling to run, etc... but ONLY when it is warmed up and the choke is open. I hooked up a vacuum gauge and it was hardly pulling anything; so i have almost no vacuum. and when i manually close the choke while it is running, it picks up rpm and smooths out a bunch, meaning lean mixture (vacuum leak). the only thing is that i cant hear or detect the source of the leak because there aren't any obvious hissing/sucking sounds at all. does anyone know where the leak could be coming from, keeping in mind that i recently installed a new carb/baseplate (stock 2 barrel equipment) and sealed the heck out of them? any help is much appreciated.