Sportsman 1000 top speed issue.

Yesterday i tried a top speed run and the quad bogged around 74 mph. (Pulling, stop pulling and then pulling again) I had her to 78 mph before racing a body and keeping her at it for 20 secs and it never did it. Could it just be bad fuel ? Or my ignition ? Just to mention . I had my spark arrestor off to see if it would help with my exhaust heat problem. So give me your opinions guys thx