RE: Loose High Speed Needle...RCV 1.20sp
Teflon tape only works when tightening a thread. As soon as you reverse the rotation you will loose the seal.
We use fuel tubing over the needle AND base to form a seal with good success. Can be a bit of job stretching it on, but when in place it will seal well for ages.
OR
Try finding a bigger 'O' ring for the needle, maybe an OS or similar.
The carby's on the RCV really do let them down (as does the exhaust).