First, I'd try to find a manual for it. If you have limited parts in your area I'd go through it to check/clean carb, reeds, air filter, and powervalves.
If you don't find anything wrong during your teardown and it still isn't better, you may be able to just go one clip leaner (raise clip 1 slot) on the needle to correct the low-mid stumble that you mentioned since most bikes come jetted rich from the factory. You can seize a bike going too lean on the needle so I wouldn't go more than one clip.