Mate my first bike was a ebay orion. I had same prob, Idle was fine and once I got over 1/4 throttle it would just splutter and bog out. Tried everything
Rewired and checked all wiring, check for exhaust/intake leaks, cleaned and blew out carby multiple times changed spark plug, CDI, Coil. I gave up and took it to the shop told them what I've tried, they pulled out a new 26mm Mikuni and whacked it on and all problems were solved. Turns out somewhere in the carby there must have been a blockage or problem in the casting which means it is good for a paperweight. I have heard of this problem elsewhere too so don't rule out the carby. Try to borrow one off another bike, I reckon 99% chance its this if theres no leaks or electrical problems.