I've got the header tuned properly. On the ST90 w/ stock muffler I tached at 10.8K rpms, with the header tuned, I'm at 12.3 (and climbing due to break-in) with an APC 15x4W prop. I cut off some more of the header and she dropped in RPM so I them slide the tune pipe back within the coupler. Believe me, I've tuned allot of headers in my time. More than I care to count.
I don't believe that it is the header nor the needle settings. That is why I was so intrigued with the shape of the low speed needle. I'll check mine tonight. If I have an extra low speed needle like I think that I do, I'll file one and try it. If it works, I post a before and after picture for everyone. "I have the technology !"
Kevin