Noob needs help

[MichaelWH]

So, barely started riding an '89 GS500 (hella noob).  Seems to run pretty well, but on the last 3 commutes I've had an odd problem show up.  I'll be riding at about 4-6k and attempt to add some throttle, and it does nothing, so I add a little more and then it starts to accel.  Shortly after that (within 10seconds or so) it starts to back fire and do some lurching.  Then after a little bit of this it dies.  I get pulled over to the side and start her back up (take a little bit of doing) and then it runs normal and fine all the way home.  I have a very short commute (4mi) so I'm not sure if the problem would recur if I were to ride longer.

So...My main question is what should I check?  I have some ideas, but I would like to get everything covered while I have time this weekend.  Does this sound like a mixture problem?  A fuel supply problem?

-I have old gas in the tank, I'm going to change it out
-All three times I've switched from On to Res on my petcock, just in case.  So I'm going to check the fuel lines and petcock.
-What next?

Thanks in advance!

[ivany]

Try running the petcock in Pri and see if it happens. Sounds like the typical GS petcock sucks issue.

[MichaelWH]

Kinda makes me wonder: What happens if the petcock is not in the perfect position?  i.e what if I have it turned at 80degrees rather than 90degrees? (say I'm trying to point at the ON position).

[tripleb]

the OEM petcock sucks at any position and often causes fuel starvation.  You're best bet is to install a honda crf250 petcock instead and cap the vacuum port on the carbs.  just make sure you get the right one as there's 2 different kinds I think.

[The Buddha]

It should work fine in that 80 degree spot just fine ... 45 degrees may be bad.
Now you could be starving for fuel independent of that. Clogged tank, clogged filter, clogged line ... dirt in carbs etc ...
You can run a few mins to over 80 before it will be starving in the situation triple B is describing.
Cool
Buddha.

[5thAve]

1st try it with new gas. Then chase the petcock gremlins if needs be.

[MichaelWH]

I definitely will get new gas in there, however, I am hesitant to blame it on that because I rode about 4 time before this started occurring with no problems whatsoever. 

TripleB: Not sure which ports you are talking about...I'm not terribly knowledgeable about carbs...

Buddha: you said "You can run a few mins to over 80 before it will be starving in the situation triple B is describing", I'm not quite sure what you meant...maybe it would help if I knew what units "80" was...

Sorry if this all seems dumb to you guys, I'm very new to this...

Thanks again!

[5thAve]

Michael, have you tried the new gas yet? Any improvement?

buddha is talking 80mph. At sustained high speed the stock petcock often doesn't flow enough fuel.  You won't notice it at city speeds.