hpergm

John, your installation does not look too bad actually.

Mine is on a scale FW190 (Top Flite), where the cowl plenum happens to be completely isolated from the fuz volume. That's why it made sense for me to do it this way. And no, I do not use the pressure tap.. Too scared, due to flammability.

Now, your Yak is completely different, very open and will not have this problem as pronounced. I would initially try to open up a couple of holes in the Monokote between the side trusses (e.g. right aft/below the wing, where it does not show) to make sure the fuz breathes/balances with atmospheric air. I will try to post a pic of what I did to my Yak for this exact same reason.

Another easy trial would be to partially restrict your louvres (towards the rear - closer to the carb) - while watching how temps behave. This will reduce the vacuum effect @ speed. Finally, you could try to just remove the positive pressure from the Keleo to the tank, retune and fly. See what happens then...