this prob isn't on the subject of ur backfire..but about the whole freeflow of ur exhaust system..IMO i would atleats have a cat not a test pipe/straight through cuz ur engine needs somewhat of backpressure and it runs somewhat better when it does have that little backpressure. having ur whole exhaust system with no cat just all straight through then it might even decrease or not even gain u hp...

 

I found the solution! I replaced the spark plugs w/NGK BPR7ES. Runs good as new.

to all who tried to help me with my problem. I appreciate your responses.

Thanks!