Yours does sound a little down on power, give it some time, maybe it will come around. The last one I did turned an 18x8 Bambula at 7190rpm the first time it ever ran with the stock muffler. This was with the stock Walbro twin needle carb off my first single ring Ryobi, the latter Ryobis with the Zama carbs seemed to be more difficult to get the proper settings on. I've tried the larger G-23 carb on this motor and there was only about a 50rpm difference (plus, depending on what mount you are using, the G-23 carb can be a pain to mount)