I have the .28 and .51 Bluebirds, both bought new off Ebay. The 21, 28 and 46 are all AAC while the 51 is ABC. IMO both of mine are very well made engines and very easy handling. I haven't had any carb problems with either of them. The owner of my LHS told me that the Bluebirds were the only engines he used when they were available here in Oz and he had the pick of anything in the shop. You're correct that they were also sold as Brat in America but I have no idea why they had to be renamed. My .28 came in the original box with instructions and their running in procedure is completely different to what's usually suggested for that type of engine, rich, rich, rich
. Sorry Dar....wherever you are
.