Backfires?

[MeatGrinder]

I have a backfire sometimes when I downshift or let off the throttle. My stock cans are partially gutted, and holes are punched in the remaining "walls". (they sound sweet)
I never noticed this with unmodded stock cans, unless I just couldn't hear it with them.
What causes this?
I notice no other real changes in rideablity, like surging.

 

[gsteve]

I get em too sj

 

[GMbusa]

I get them once in a while on my 04'.

 

[Bence's Busa]

i would remove pair valve.

 

[bbbsleeper]

I have punched my pipes a ton, but know backfires, pair valve is gone though.

 

[NearDeath]

pair valve mod fixes the mild backfire...

bbbsleeper... you may have a different problem, but in general this issue is fixed by either removing the PAIR or you can plug one the hose off teh airbox which goes to the PAIR and I beleive this will fix it too... It is one of those hoses anyway...

 

[BA BUSA]

With less back pressure it might be to lean now.

 

[BusaFever]

I had the same problem, ordered the pair block off plates from Tom at Veltune.com
Fixed the backfires right away.
You need to remove the pair valve soon, or it can damage your engine. I got a buddy who had major engine problems because of the severe backfiring.