I flew Fox 35's a lot back in the late 70's, early 80's. Could not get the Fox NVA to work consistantly. Put in Super Tigre NVA and all is well. Never got around to opening up the venturi as mine ran to suit me as they were. Fox changed the NVA design to be more conventional, pointy needle rather than flat, after it was noticed that most Fox engines seen at contests did not have Fox NVA's. Replacement NVA's are a noticable part of engine sales.