GYTR pipe, backfires constantly

I've been searching for quite some time but I can't seem to find any real answer so far.

I have installed a new GYTR exhaust with the stock header - no leaks that I can find. (Performance was severely rubbish, much worse, down low, I was thinking of going back to stock until I got the EFI programmer in...)

EXUP removed, AIS disconnected (still awaiting the removal kit, so I just unplugged the electrics)

Flapper taped down, flapper doohicky removed (leaving the new hole in the airbox above the flapper door).

Checked the CO settings, they were set to 0.

I have tried taping up to flapper doohicky hole up or leaving it open, disconnecting the O2 sensor and leaving it on, I've added an attitude EFI programmer (stock settings), gen 3.5, having it on or off, no matter what I do, every time I let off the throttle, the bike backfires (flames coming out the exhaust, big bangs and cracks etc)
It sucks, I don't want to set the forest on fire when I'm riding, I don't like the noise, I hate the attention it gets.

Around the exhaust pipe, there is a ring of gooey oily crap.

I'm at a loss as to what is causing this and how to get rid of it. Should I be richening it up?
Two mechanics at the shop are of completely different opinions - one says it backfires because it's too rich, it's the excess unburnt fuel which is igniting - the other says it's because it's too lean.

Halp!

So, you have not yet eliminated the AIS, correct?

I've not removed the tubes/pipes, I've only disconnected the electrical wire from it. I was under the impression it'd be doing the same exact thing, isn't it?

I don't see how these AIS removal kits would sell if it were the same thing.

Also, if you removed the airbox inlet flapper solenoid (doohickey), did you plug the small hose running to the throttle body?

I read on the forum someone recommending simply disconnecting it to see if it did what one would expect before going and removing it all. I'd have thought the AIS removal kit was similar to the EXUP emulator which costs $50 for something that can either not be needed if you leave the EXUP servo in (tucking the wires out of the way) or can be done with a 10c resistor. If there's no juice going into the AIS servo, how can it still be pushing more air into the system?

I did plug the hose running to the throttle body.

When cruising at low revs it seems to be fine when I let off the throttle, no backfiring. When I whip the throttle and let off, flames and bangs galore. I'm thinking I must be running rich on acceleration in the higher revs?
It only backfires when I let off the gas though, there's no mapping for deceleration on these EFI programmers.

The AIS does not push or pump air into the exhaust.
It is an electrical/mechanical solenoid that opens on cue to allow naturally-occurring vacuum to draw air into the exhaust pipe to supposedly better burn exhaust gas.
This air comes from the airbox, and there is a hose running from the airbox to this solenoid.

So, does disconnecting this electrical wire cause any problems by allowing the solenoid to be open all of the time, or at least open when it is not supposed to be?
That's what I'm wondering.

Deleted.
Double-posted for some reason.

Thanks for all the pointers. Turns out the solenoid is wide open when it's disconnected. Wiring it back up solved it completely - the removal kit still hasn't arrived, so it'll do nicely until I can stick it on. I should've started with that and ignored the forum posts where they suggested disconnecting it in the first place...
The pipe seems noticeably quieter too which is much appreciated and the bike runs a ton better with the EFI programmer back to factory recommended settings.

Glad you found the cause and reported back.