MMMMMMM. Could be a blob anywhere in the fuel system. Bad real engines have that symptom when the fuel filter starts to get blocked. Fits you to a T.

Bad fuel mix load ?

blobs come in clear & long skinny sizes also. no joke. That opening the needle routine sounds like slime going back & forth. Next time it does it . leave it running fast on the ground. open the high needle more & more till it is almost loose. Put a piece of flat stick SAFELY over the carb inlet. It should suck the slime thru or clog it so bad you will know where the problem is.

Post when you find the problem.