I'll go with NTFDAY's suggestion on the metering rods.

I had a bent one in a new carb that stuck open.

Symptoms were different - overly rich.

Take the rods out, remove the piston, roll the rod on a known to be flat surface with the short leg hanging off the edge.
If they're bent it will be very visible.
Use care in straightening them.
Use a lot of care when re-installing.

Carter/Edelbrock metering rods richen up the mixture when engine vacuum levels reach a point determined by the springs.
Big cams take a lighter spring due to less vacuum.
If the proper springs are not in use, the metering rods come up early, the car idles rich and runs rich at low speeds.

Go to the Edelbrock site, get the jet & rod numbers for your carb and check to see if they're right.
If the carb was new, not a problem, but if it's used someone may have made changes that don't coordinate well with each other - rod & jet wise.