It's a bit more detailed than that, too.  It's a 1993 GS500, if that helps.  My bike started having odd hesitation issues last week on the ride home from work.  It was barely noticeable but it was alternating between going normal then losing power for a split second (thinking it's a cylinder not firing properly).  When I let off the gas to slow down on a curving exit, the bike died on me.  I only sat there for maybe a minute, fired it back up and it ran fine the rest of the trip (sounding fuel related?), not that I had far to go.

Over the weekend, I did a full service I was planning on doing anyways:  valve shims, oiled chain, new plugs, new intake.  Have new oil filter but haven't changed it + oil yet.  Took it for a spin, a few miles in, the same problem happened, bike wasn't going smoothly on the interstate.  Went off the interstate, and it was stalling when going down to idle until I choked the throttle.  Briefly got back on the interstate, and just before making the exit home it really felt down on power.  Bike hasn't been driven since then.

I pulled the new spark plugs today, one looked fresh and fairly normal.  The other was dark, coated in carbon, and the gap seemed way to small.  Definitely smaller than the other plug.  I remember looking at the gap before I put them in, but didn't check them too seriously.

Not sure what else could be going on, would appreciate any assistance.  I haven't touched the carbs.  I might have turned the petcock from prime to reserve before this started happening.  It might have been after, too.

I would try the gas cap vent cleaning (sticky here). Doesn't explain the difference in plugs but it could be the primary issue.

regards
Mech

Try new plugs. Once I had a plug go bad with an intermittent internal crack.
also check your plug wires. they can get corroded or come unscrewed from the coil or the cap. Sometimes trimming off 1/4" on each end of the wire and screwing them back in makes a big improvement.

Those are the same symptoms I experienced with fuel starvation at highway speeds.  The forum folks recommend flipping the frame petcock to prime when it happens.  I tried that and it worked!  Good luck.

If you rejetted which causes increasedd fuel demand, it can happen. The frame petcock is designed for a certain maximum fuel delivery.

On the other hand, it could be dirty. open it up and clean it out.

Last, the vacuum line could be clogged or the vacuum port on the carb could be getting clogged.

I have never encountered a defective frame petcock, but have encountered dirty ones.

Oh, and you could be low on gas. The tapered design of the tank is deceptive when you look in. When it appears half full, you only have a gallon left which means switching to reserve fixes it. (Prime uses the same line as reserve.)

Thanks for the responses.

I might have changed the petcock away from prime before this started happening.  I'll be sure to test that and cleaning the gas vent & see how it goes.

One thing to note: The only tubes connected to the gas tank were the two fuel lines for fuel & reserve.  There was at least one other nozzle with no hose ( overflow tube?) in the center of the tank.  And based off other diagrams / pictures, shouldn't there be a 4th vent tube?  Maybe I'm not looking at the same year / model.

Your fuel line configuration sounds correct.  My bet is it's just a fuel starvation problem. New fuel lines, clean petcock by disassembling and if carbs aren't clean, thoroughly clean them and blow out passage ways.