Mark, I’d go up a full jet size instead of float arms and needle clip changes. If for no other reason to just see for sure if its too lean. That said, from what I’ve experienced an engine too lean will miss on the top end and pop. And since your’s is not, I can understand you trying the needle clip. Also regarding the choke, when you apply it you essentially richen the mixture across the board. Another reason to go up one main jet size.
When I had issues in the rev range you mentioned, it turned out to be battery related. So you might look there if the main jet doesn’t solve it.
Other Rotax check points: if the fuel pump diaphragm is old you might inspect/replace that and be sure all your fuel and vacuum hoses are tight and secured. Sometimes air can be pulled into the fuel lines. Or the pulse line can lessen the fuel pump’s capabilities.
Is your problem occurring all the time at that rev range? Or perhaps just when exiting a corner in that rev range?
Something suspect is the 7-8k rpm mark. That’s defiantly RAVE valve suspect range. I know you said you checked it, but don’t 100% rule it out as you step through other areas if jetting doesn’t work.
Lastly, as John Savage would advise: if you can swap carbs with a known good one, you can then begin to backwards trouble shoot. If you swap carbs and the problem still exists, I’d start looking at electrical.