Do you have all the vent holes empty Phil? I currently have a 15 Eyra with 27 fury that blows out very bad right before it gets up all the way on plane, no poles loaded with hydro plate and trim all the way down. I keep trying combinations with the pvs holes but as soon as I do that, then it isnt getting enough exhaust and will take forever to plane off. I have thought about getting some extra 5/16 holes like you did and and that would allow me to lightly plug 1-2 but I am not sure. I am going to keep trying different things.