JD had this happen to him on the way back from Kentucky Lake. I was riding behind him and noticed his back tire suddenly squirm, he's on the highway and starts slowing down. I ride up beside him and point to his back tire that was going flat. We pulled over fully expecting to find a nail or something and couldn't find a thing! Ok, so I doubled back to a Walmart, picked up a little compressor and we aired it up again.
We head out again and about time JD got up to speed.. poof.. tire goes flat again! What the heck! so we pull over again, gigure we'll have to male the 368 mile trip home in 2 mile increments when we discovered that the valve stem was leaking.
With the rubber based 90 degree stems they apparently catch some air at highway speeds and this in turn starts wearing on the rubber base. That is why he tire aired up fine, but once we got up to speed it would go flat again.
We pulled into an Advance Auto after a call to Jason to find out what was available. They loaned us a big C-clamp so JD could break the bead and get to the valve stem. Replaced it with a metal based stem and we made it home just fine (Always a little iffy when you break a bead on a tire and you pray that it pops back in ok when yuo pressure it up!)
So.. ESPECIALLY if you have the angled stems, make sure they are the metal base stems
Patriot Guard Rider
2000 VN750 Sere (Serendipity)
1990 GL1500 (Ole Blue)
1986 VN750 EVie (project bike, heavy custom)
VROC # 11628 / 25000-H
ARVROC # 12 Coordinator and Crowd Control
OKVROC # 18 (H)
TNVROC # 45 (H)