This problem started out of nowhere. Went to take the car for a drive about a month ago and it had a horrible part throttle stumble/miss. It would clear up under harder acceleration. Also the target AFR in the Holley is 14.7 and it was constantly running 17.5-18 and it was dumping fuel trying to compensate. Swapped out the plugs hoping it was just the 5 year old plugs in it, but it continues.Started to leakdown test the motor last night, but found no problems with the driver side cylinders and called it a night. All the plugs are black again from the Holley trying to compensate the lean AFR.

 

There's a forum for issues such as yours....

 

Cracked Y-pipe, sucking AIR prior to O2 sensor.
Yep, Holley will pour on the fuel.