Andy wrote:The power jets are "progressive", so the wider the throttle opening, and the higher the RPM, the more the intake "draws" on them. That's how the standard setup can run such a small main jet (giving a crisp throttle response) and not go lean at the very top end. Basically, it just gets richer and richer as the revs rise.

Hopefully you've found the problem.

First time of working on a power jet carb (or secondary main jet carb), and I wondered how it worked.
How does it draw then deliver fuel? I guess through some galleries in the carb body next to the slide...I am also intrigued as to how it can deliver a variable rate of fuel without the needle influencing it?