reaper, odometer is reasonably accurate? The vent issue is not unique, but switching to reserve was never what led to the fuel starvation/release cap to restore fuel flow. Fill tank and take a steady ride with minimal stop/go and no "racing" for 50-60 miles/kilometers and fill tank to as consistant a level as possible. Do the math and repeat process. After a couple of runs that you control most of the variables you will get a reasonable average fuel use to work from. It sounds as you may have a petcock that is clogged/installed at the wrong height and maybe a pinched/clogged vent. You haven't posted (or I missed info) the actual fuel amount added at the distance driven. This is really the data needed to diagnose the issue. Your bike would be mainlining gas and as others have posted, it just wouldn't be able to run that much fuel.
Good luck.
BobW
