hey guys. i got the car running great, timing is dead on, starts right up with one pump of the carb, sits on fast idle and then i kick it off once the choke is open and it idles fine.

ive adjusted the idle mixture screws by turning them in 1-1/2 turns and slowly advancing out until i reached the highest vacuum, adjust idle speed back to around 900rpm and then check vacuum again, i then turn them in an 1/8 turn for “lean best” as edelbrock states. i always make any adjustments on a fully warmed engine.

the car runs great. my issue is that over the course of lets say a month or two, it’ll gradually start idling lower and lower resulting in me having to turn the idle screw back up to the 900rpm that i want it at. over the course of this month it crept down to around 750-800rpm, i had to bring it for an alignment today and it was somewhere around 700rpm. all of this is based off of the engine at operating temp.

is this just a typical edelbrock/carb quirk that i’m naive to? the temperature in new england fluctuates decently so maybe an air density thing? it was relatively cool a few weeks ago and then these past two days have been very hot.