I, like many others, lost their idle screw early on. I made the mistake and found another screw that fit in, but it was so long that when I buried the screw it actually bent the carb needle! But anyway, that's getting off on a tangent.
The spring on the stock idle screw simply doesn't do enough to keep the screw in place, so a lot of people lose their screw because of vibration. If you've been around the MB community enough, you might have heard of making a "safety wire" so that the screw doesn't get lost. I think this idea takes that a step further.
A wingnut and a rubber washer keeps the screw in place! Theoretically, this would mean you wouldn't have to worry so much about adjusting the screw because of vibration. When I get a new idle screw, I'm definitely going to be doing this. You might even get away with using a spring washer if you wanted.
Replacement idle screws can be purchased at thatsdax.com.
You might also be able to find a compatible screw at a lawn mower store.
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!