Just wondering... is that the answer you give if someone doesn´t appear to have the knowledge required to fix the problem? I had one with the same symptom, that is, it would start and idle but wouldn´t rev unless I put on the choke. I found the main jet was blocked. Cleaned the carby and unblocked the jet and Viola! it works like a charm. Don´t know how to disassemble the carby? Get a manual or just play. Be careful though as the parts can break if forced/seized. use antiseize to free up difficult parts instead of forcing them. Good luck and happy learning.