Moped Army

Ok.. So i just think the Bullet needs some lovin' and be ridden. I took it all apart last week and put it all back together. When I first started running it, it kinda struggled now it runs awesome right when I first start it up. Fast off the line and switches gears smoothly. after about 10 minutes of riding the acceleration cuts down alot and sometimes it will take a while to switch into second gear. Now I am thinking that a new air filter will correct this. I have never replaced the air filter and i tried to clean it but light still struggled to pass through most of it. do you think the air filter will correct this??????