I recommend having both vents, the new tank and the cap. I initially built mine without the cap vent and was having variable fuel pressure when the tank was filled. Put a vent hole per instructions in cap and no problem the last 100 hours.
Scott- 2018 dues paid
Got medical back, now building a 7A.
RV-12 #120515, 319RV 1st flight 12/2015 now over 260 hours.
RV-9A, 536 hours sold, RV-7 sold, Kitfox sold