2mm will make the different already. More air to go in to the air chamber and combusion room. That's why some bore it until 64 or 67mm... After market TB like Jun is 70mm at inner diameter. But bigger doesn't mean better, big enough for ur engine OK lar. Don't tell me a stock b16a is going to put a 67mm or 70mm TB.
just did some did and tested my DIY VS using 12v batt. everthing is o.k, LED indicator light off when charging and on when fully charged. when removed the power supply (12V battery), the LED remain on... let the VS...