even though i don't hear anything in the tank, i'm assuming the reserve tube broke off of the petcock because i found another post here that reported that that was a distinct possibility. this means i've been pumping unfiltered gas into my carbs whenever i jump to reserve.
rather than buy a new petcock, i bought some small plastic inline fuel filters and some extra hose and rigged them up on both of the gas tubes coming down from the petcock. so far, so good. it took a while to get her started, but she's now idling perfectly around 1100rpm.