Yesterday I took my '90 GS out for a ~30 minute ride with a passenger doing about 40-45 for most of the trip.  Coming home on the highway the bike started to lose power at about 55 mph and acted like it was out of gas.  I downshifted and went down to about 30 mph then power regained...this happened about 3 times.  Then today I took it out myself and was riding for about 5 minutes, once up to ~55 mph the bike lost power like yesterday so I came to a stop and couldn't get it started.  I trailered it home and it started right up.  Does this sound like a carb issue?  I had them rebuilt last season and drained them over winter.

Thanks for any info you can provide,

Jason

Sounds like the tank vent to me. Could also be the upper vent hose.

http://gstwins.com/gsboard/index.php?topic=41061.0

I had a similar episode but was out of fuel.  I turned the petcock to 'RES' and got to the nearest gas station and filled it up and the bike ran fine after that. Your engine sounds like it isn't getting any gas somehow.  Maybe a clogged fuel line?  Does it sputter and quit or quit all of a sudden?  Try pulling off the fuel line to the carbs and see if you are getting gas to the carbs.   If you are then maybe it's an electrical issue. 

When you try and start it, does the exhaust smell like gas?  If it does then you are getting gas to the carbs and the cylinders are not firing.  If it does not smell like gas then your problem is fuel not getting to the carbs.

Good luck.     

I would say fuel starvation. Just use search and you'll find tons of info about that issue
What year is your bike?? is it pre 2004?
if the bike is post 2003 it is NOT fuel starvation (the petcock has been redesigned for 2004 and up)