The TYM T264 uses the Kukje A1100 from what I've read online.
That Kukje A1100 engine is used on the Branson 2900 and 3100 here in Europe. The 2900 has 28 HP and the 3100 has 30 HP, however both have a turbocharger to get this HP increase, maybe injectors and definitely some changes on the injection pump.
I'm sure you can squeeze a bit more HP but just playing with the fuel screw on the injection pump. It's a like a VE injection pump on a Cummins 5.9 and several other engines.
By the way, I'm sure you know doing these changes will void warranty. The fuel screw has a tamper proof cap that can be somewhat of a pain to take off.