I've got HKS racing suction, re-amemiya header, catback and amuse exhaust on my 2008 rx-8. After all this installation, my 1st gear is running perfectly smooth. However, during my 2nd gear, at around 7000rpm, there is a popping sound which makes the car lag at that point. I could try to push hard to get through the popping noise after 8,000rpm but am afraid i could damage anything. The 3rd gear gives me the same problem too.

How do i get rid of all this? Has this got to do with the carbon build up?

Need your advise.. Thx