What do you mean "weak"? It routs the exhaust out the back instead the front, it works, and there's a slight gain in upper-end power.
The GXH50 is a 2HP, 2ft/lbs of torque engine, it's powerful enough to move you down the road, but it's not exactly a powerhouse, and doesn't really have the potential to be. Like the Huasheng clone, it's a pretty reliable little workhorse.