So….more header talk….this had me scratching my head

MOPAROFFICIAL said
Yep. The scavenge effect.

MOPARMAGA said
Because you lost exhaust velocity, it built a low pressure wave at or near the collector which did not get evacuated completely, it just sat there until and was partially sucked back into your intake charge.
Not enough fresh air paired with all that fuel caused rich mixture.
I believe darin Morgan and hooker headers told me that in my reading

Actually, if it goes lean with a header change you can bet the header isn’t functioning correctly.

When you change from one header to another and you have to take jet out (because it’s rich) you know the header is doing it’s job. There is a reason for that and it’s important, not only for header function but any time you do work on the induction or exhaust. Any time you have to take jet away (for the most part) you will make more power and be quicker and faster on the track.