So here while back i purchased a 89' gs500e and it had been laid down so it had a lot of problems. levers, handlebars, rear sidecovers, blinkers, tank dents, etc. im in the final stages of getting the bike running and after looking under the tank i noticed that the bike was missing its petcock, but it still had its fuel chicken on the tank. my question is can you just run a line from the fuelcock to the c

to the carbutor and the bike run normally? Thanks

So it is missing the secondary petcock that allows you switch on/prime/reserve? If so, I believe you need that for some vacuum effect, but I could be wrong.

Yeah, but in the race modification section of this website theres just a single fuel line running from the fuel chicken to the carburetor...so what happens to all those vacuum lines?

well I am no expert by any means but the petcock is there for a reason.
So just by thinking logically:

1. your main operating position is ON, which means that it uses vacuum to suck the fuel from the tank as needed

2.  when you switch to PRI the carburetors are gravity fed with fuel, and people say that you can't leave your bike with the petcock in PRI because it will flood the engine with fuel, which may have nasty consequences.

3. You will also be missing RES position without petcock

Your best bet would be to go to eBay and buy used petcock from 2004+ GS500F.
Those petcocks are better than pre 2004 and do not cause fuel starvation issue anymore.   

Vacuum line isn't the problem, it can be capped easy. The stock tank petcock has no way to shut off fuel flow.
People mod race bikes like crazy, it could well have a pingel or a savage or other petcock that will fit the gs tank and has vacuum dependent flow.
Cool.
Buddha.

That vacuum line does nothing but pull back the rubber seal inside the 2nd petcock to stop the fuel when the bike isn't running. All of the gas is still fed by nothing more than gravity. You can definitely run a line straight to the carb. The only thing you'd have to work out is the fact that the stock fuel chicken in the tank has 2 lines coming out of it, one for normal flow and the 2nd for reserve. You could cap the normal one and run a line straight from the reserve to the carb.

The only problem you'd be left is the possibility of the fuel overflowing if the carb float ever got stuck. You could put an inline on/off switch somewhere you could reach it. You could probably find one at an auto parts store, or else online for a few dollars.

Thanks everyone. That helped a lot!!!!