Thank you for all reply.
My air cleaner is an oval type.I exchanged it with new one,It didn't improve the issue.
5th gear ratio is 0.68,and Final drive ratio is 3.444.
I drove at the racing track so I needed to upshift to 5th gear.I could't downshift to 4th.
"AFR is low". I also think so.Yesterday I changed main jets to small ones.I'll take care not for braking engine.
https://youtu.be/1jj0ltsJqVI