Originally Posted by prigai

As av8tor1977 said it is a "weedeater" brand, most a likely 25cc engine.
As stock they are not very strong but they are very light and can be improved. As mentioned the easiest way to improve is by:
1. Changing the muffler, or at least remove any internal baffles and increase the size of the stinger (outlet).
2. Changing the carburettor, the standard venturi size is often around 8mm (size 20), the correct size is 11mm (size 28), but size 24 (9.5mm) and 32 (12.7mm) will also work.
3. Suitable props for this airplane (floater type) and engine are 16x6 (fastest - around 8000 RPM), 17x6 or 16x8, even an 18x6 will do better than an 18x8, but it will be more responsive with the smaller props.
4. If you are a bit technically minded you can also do some ports work, in standard form this engine is very mildly ported.