ORIGINAL: The Raven

Definitely get a two needle carb, specifically one with full adjustment ranges.

For example, the Zama carbs that come on many Homelites appear to have two needles covered by a plastic limiter. Even with the adjustment limiter cut off you'll find only one needle is really adjustable.

To get a full range of RPM you need a two needle carb with approximately 11+mm of venturi. A WA167 does this at 11.11mm.

A member in my club has put a very large Walbro on his Ryobi and it runs better than any other conversion I've seen. Very reliable setup with well over a 100 recorded flights. I intend to identify the carb model for myself and, so I can share it with others here.