+1 on cleaning out the high speed needle jet. Any little bit of gunge in there can cause major problems. Remove the high speed needle and flush out the housing with fuel. Check your needle O rings are in good shape too.

Tuning wise on the short needle version, bog like that would normally suggest the bottom end is a tad lean, but thinking a bit more about it, if it's only doing it below half a tank then I am favouring it being just a fraction too lean on the top end (as the HSN is the first needle in the fuel system to offer resistance to the fuel flow from the tank, especially as the tank level drops and it's harder to pressurize when you quickly open the throttle). If this is the case normally just richening by an hour or two will be enough to solve the problem. The top end needles are very sensitive on these motors, so going too lean on the HSN is not hard to do.
I doubt it would be the pipe. The 086 is mint on the 3 and 5 Port motors. I have never actually run one on the 7 Port, but I remember someone on here using that combination and liking it.