Hi guys so i have this weird backfire/afterfire on acceleration on my z900. I just installed akrapovic full system last month, it does backfire @popping on decel which i found its pretty normal, but now after riding for couple of weeks i notice when im riding at higher rpm mainly in gear 4 at around 9k rpm when i let off the throttle for one sec and i start accelerate again i heard it backfire once. And it occurs everytime when i did it again. But i dont get the same backfire on gear 1,2,3,5 and 6. What do you think causes this? Exhaust leak, too rich or too lean?