Get rid of the 30mm nibbi. That will solve all your problems. It's way too much carb for an otherwise stock cg250. I have a fully modded engine, cam, big bore, ported head, and I run a vm26 clone, which is basically the stock carb, but with Mikuni jets. Example:
https://www.amazon.com/Hessenboom-Mo...%2C166&sr=8-31
If you absolutely must keep it, your pilot is too big. Use a 35. At most a 38. If you are stock a 115 main should do the trick, but with the PE30 having reduced velocity it often requires much bigger jetting than would be normal, so maybe have a 120 on hand as well.