Sorry guys just bought a used 1992 gs500e with no carbs. Got a used set on line here from a member and installed them along with new air filter and spark plugs.   Tried starting it last night (bought bike as a learner for my 16 yr old son) full choke/bike on prime and it fired and rev up to about 4 k rpm and ran about 20 seconds then died, Kept doing this cant figure it out. Positive I have the fuel lines routed correctly used diagram from here. My son is very disappointed would appreciate and suggestions on problem or trouble shooting it. Thanks in advance. Bike has 15k miles on it.

Could be a problem with the vacuum petcock and venting of the tank. Mine has this problem. Try opening the gas lid, leave on prime and turn it on. If not, your floats may be incorrectly cutting off fuel while operating.

Thank you so much for responding I really appreciate the response and help! I will give it a try when I get home from work to day.

Better yet, eliminate the vacuum petcock problem to isolate the carbs to make sure the carbs work. All you have to do is get a "t" connector and join the two nipples under the tank, then go to a valve ( that you can cut the gas off when you're not running or else it'll flood your carbs) the to the carbs. I have this setup on my bike currently because I can't get enough vacuum petcock to operate well. That just means I have to remember to close the fuel Valve when I park my bike no big deal to me.  I had the same problem with my petcock, set it on prime for a minute, then start it bike up, 2 minutes later the bike acts up, revs up and then dies. Set it on prime and the bike runs all day. So I just eliminated my vacuum petcock. But just give that a shot and get your carbs working and make sure there aren't any problems there. Once you've done that, you can slap that vacuum petcock back on and work from there.

http://gstwins.com/gsboard/index.php?topic=58895.0

Any other ideas?

Ok finally got my sons bike started today. very hard to start cold finally got it going with full choke after it was warm from trying. rpms kept bouncing around up to 7k down to 1100 and would die if any throttle was added. would not stay running with anything less then full choke even when warm. opened gas cap so not a fuel breather issue also ran in prime or any other position. Confused please help. Thanks

Did shoot video but I am having trouble attaching it.

bump      any suggestions guys? novice here. 

Needing full choke means you are running very lean. I'd look for a leak at the carb boots first. Are you sure all the vacuum hoses/plugs are in place?

yes doubled checked all vac lines. but did not double check the boots (carb to engine and carb to airbox?)

Yes, spray wd40 at the boots (if you can get the bike running) and off revs increase, the bike is sucking air in at the boots.

I will give it a try

Also, have you checked valve  clearance? This can cause all manner of symptoms.