Who needs to fiddle with two screws every time just to get to the air filter? This simple mod to the carburetor makes the size of the carb a bit smaller(for those who need frame clearance) and makes it easier to add/remove an air filter! It looks like adb140275 from motorbicycling.com removed part of the air filter cover and zip-tied a piece of lawn mower air filter material around it. To make this mod even easier, you can use a "quick release" zip tie so that you don't have to cut it every time you want to change it!
EDIT: I have a similar setup, but instead of the foam I use 3 layers of knee high stocking. At Rite-Aid, you can get a pair for just a dollar. Makes a nice high-flow filter if you're riding in an area without a lot of dirt!
A warning to those looking to mod their motorized bicycles:
Most, if not all, of the hacks and mods featured on this site were made by individual hobbyists. If you are new to working with 2-stroke bicycle engines, please by aware that there's a possibility that a mod featured on this site could seriously damage your engine. Please don't try any mod from this or any other site unless you fully understand what you are doing. The owner of this blog will not be held responsible for both material and bodily damage caused by performing a modification featured on this blog. Also remember that opening up your engine may void your warranty!