No stuffers , no rev boost and a little lower rpm ....i went to check out some info and found a post by Bob (Spike 60) put on AS. Another bit of info is 'How" and "when" rev boost works on the 550 and 560. You all probably know this ??. I still maintain that this 550 running thing (some ok ..some not) is not logical if the parts are ALL the same within the generations of saw and part of the final upgrade on the AT-12 from what I can see has put a new kit in the carb .
My reasoning on the situation is that ...the AT side can only work properly if the "hard parts" are ok to do the job . In my humble opinion.