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 over 235 hours.
1st flight 12/08/15, flew SNF, Oshkosh, Triple Tree & SERFI in year 1!
RV-9A, 536 hours, sold, RV-7 sold, Kitfox sold