One observation......needles and seats always look new, even when they're stuffed.
And the O ring seal isn't supposed to be re used.
Is the float floating ?. When you push it down with the cable tie, it must lift immediately.
Is the float spring correctly in place beneath the float ?.
Other than the above, I could scratch out a page on Holleys and still not pin it down, as it could be a host of things causing the bog down. Most likely its flooding though, as the correct fuel level in the bowl is vital.
I'd try again with a brand new needle and seat, but if it's not OK, then it's probably going to need to visit the sick bay of the local carby shop.