Got my bike out of the shop recently and the bike had sit for about 2 months.  I tried to start it and it ran for about 5 seconds.  I turned the choke on and it died and wouldn't start again.  You could hear the starter going just the engine would not turn over.  Thinking maybe the battery had lost its charge I charged it overnight and tried again.  Nothing.  Called my local shop and asked for advice.  Said 9/10 times you have bad spark plugs.  Replaced those.  Got closer to starting but all you hear is the starter.  Tried starting it in all 3 petcock settings (on, reserve, and prime).  On reserve it started for 2 seconds and died.  Any advice?

If the bike has been sitting for awhile, the fuel in the carburetors will likely have evaporated. I'd put the bike on PRI and let it sit for a few minutes. This will give the carburetor float bowls a chance to fill up (listen for the fuel flow). Once you have done this, try to start the bike again.

If it runs, problem solved (change the petcock setting back to "ON"). If it still won't run, come back and let us know.


edit: changed "reserve" to "PRI" (thanks simon79!)

+1.
Rather than RES, I'd try on PRI (I'm pretty sure beRto meant that ), and leave it for a minute or so before attempting to start the engine.
PRI bypasses the vacuum shutoff system and lets fuel flow free into the carbs.
Oh, if the bike still won't start, don't forget the petcock on PRI. Leave it in ON or RES.
Leaving the engine off with the PRI fuel setting may be harmful.

RyanClarke said he tried all 3 positions on fuel selector valve including PRI.  Don't know what they did in the shop but I'd check that fuel shutoff on the bottom of the tank first, could be the gas is shut off there.

^^^^^^^^
Yes, might be the tank shutoff valve as well.
As for the selector valve, maybe the float bowls are empty, and even though Ryan tried all three settings, he left the valve in PRI for too little time, not allowing the bowls to properly fill up. Just my .02.

Well, let's wait for Ryan's feedback.

Got home from work and tried your suggestion of leaving it in prime for about 5 minutes before I tried to start it.  Tried starting it in all 3 settings, and now my battery is just about dead from trying to start it so many times.  Where exactly is this shutoff valve?  I called my mechanic and he said he didn't touch it but I'd like to give that a try for shits and giggles.  Going to charge the battery up again and see if I have any clogs in the fuel lines but after that I'm out of ideas.  I have battery spark fuel and compression (seemingly for all 4 haha) so I don't know what else could be wrong, and i don't want to take it to a shop again and be without it for more time and more $$$. Any and all suggestions are welcome.

Easy to check shutoff.  Take off seat, remove 2 screws one on each side that go thru frame from outside to hold the bracket that holds the rear of the gas tank, lift up the rear of the gas tank and stick something under there to hold it up a few inches.

Look under the tank from the right side over to the other side where the 2 gas hoses connect and you'll see a slotted screw head there.  The slot is vertical when on and horizontal when off.

If you have a 2000 or older model you have to pull the body side covers out a little to remove the bolts holding the gas tank, 01 and later the panels don't cover the bolts.

What was your bike in the shop for?

How do you know you are getting fuel, air, spark, compression?

Have you tried draining the float bowls to remove the old gas from the carbs? Once drained, put the petcock on PRI for a minute or so to let the carbs refill (you should be able to hear the gas flowing - or you can redrain afterwards to confirm fuel was getting to the carbs).

A follow-up on the shutoff valve....

I checked your posts, and it looks you own a '96.  This photo of my (identical except for colors) '99 was taken from the right side of the bike without taking anything apart.  The in-focus item in the background is the shutoff valve.

As gsJack said, if the slot is horizontal the flow has been shut off.  If the slot is vertical (as pictured) it should allow fuel to flow from the tank.

Well it's been a month but I've finally gotten a few nice days here in Colorado to work on the bike.  Charged the battery, drained the fuel tank, drained the carbs, added some carb cleaner to my fuel and she finally started.  Now, new problems have arisen.  It'll start with the choke on and if you give it any throttle it dies.  I let it run for awhile, turned the choke off and twisted the throttle and it died again.  I let it run for like 15 minutes and twisted the throttle and it would rev, but it was VERY slow and sluggish.  I let it run for another 10 minutes and went on a ride through my neighborhood to test my newly installed Katana wheel and tire and it ran but really slow and sluggish.  Throttle response was very slow and the bike had almost no pep, and that's also with my newly installed 14t front sprocket.  My instincts say gunked up carbs, but this is my first bike/car with carbs, I've always had EFI.  Any suggestions?

I have the same problem currently with my 96 model.  Have had the carbs apart, checked for blocked breather hose, etc.  Have spark and compression, but it does not want to continue running, and now it won't even start.  Obtaining a set of m/c juumper cables and connect to car/truck battery should help you from draining battery.  Let us know if you find a solution.

UPDATE:  After going into the carbs for the second or third time, I removed the needle jets which I had not removed on previous disassemblies.  Noticed that at least one of the needle jets was missing an o-ring where the main jet screws into the bottom of the needle jet. Replaced it along with the o-rings on the underside of the slide carriers - one being pretty deteriorated.  also changed oil with new filter and new plugs.  After testing the slides for proper operation with a vacumm cleaner, i surmized that the source of the problem was the engine was generating no suction.  Fuel was not being drawn into the engine.  This was confirmed by my friend James who suggested squirting 10W40 oil/Marvel Mystery Oil into the cylinders to establish more suction/vacuum, which it did.  The existing oil may have been diluted with fuel over the years.  The bike now starts and runs GREAT;  1,450 miles on bike because no one could get it to start over the years.  Cheap commuting . . . here I come.   I appreciate all posts on similar topics which has enabled narrowing to a solution.   Also eliminated the vacuum function of the frame-mounted petcock.

Update...I started her this morning in the hopes that the motorcycle gods worked a miracle overnight and she would be fixed and fast and fun again.  Not so much.  She was better though.  I started it and twisted the throttle all the way open and the revs jumped like 100-200 RPM but that's it.  Yesterday when I twisted the throttle after first starting it she would just stall.  I continued to hold it open and they would jump 1-200 rpm every 5-10 seconds or so until it got to 3,000 and it started to climb, but still at a VERY slow rate.  I would say the tach rises like I have the throttle on a healthy bike 1/4-1/2 open.  It got up to about 8,000 and hesitated, then got about up to 9,500.  Not wanting to do any damage I let go of the throttle, and the revs dropped and when it hit about 8,000 I heard this loud pop (I assume it was a backfire) and it went back down to idle.  Not really sure what that means, but just giving every bit of info I can to point me in the right direction to fix it.  Any and all help would be greatly appreciated (this forum is fantastic by the way, you guys help a lot).