leaky carb?

Hey guys, i have a problem. Its on a honda tho. When i park it on the sidestand it leaks gas out of the vent tube of the left carb. Yes, left the gas "on". Petcock is vacuum operated, thinking this shouldnt be happening. But if i turn the gas "off", it stops leaking immediately.. I did recently replace the gas tank, and the screen that goes over the petcock tube that goes into the tank was wasted, so i did without it. 30$ online for it. Thought that was a bit much, but is that my problem? Really??
The lines, vent and vacuum are in the right places and securely connected, the bike runs fine. And ya, i know, turn the gas off dummy..but im a forgetful guy.. :whistle:

Your vacuum actuated petcock is shot. They're among the first things to go on older bikes. There are rebuild kits available but I wouldn't bother with them just get a new petcock.

KZCSI

Ya, was thinking it had something to do with the petcock. Should have added that is doesnt work on reserve either now.
Ive seen replacement ones in dennis kirk, universal, but know if i saw a vacuum operated one. Assuming I could just switch it out and not worry about the vacuum anymore? And the vacuum line to the petcock, plug that up? Thanks by the way..

A vacuum petcock will NOT have an off position... will be PRI ON RES - if the petcock has an OFF position, it is gravity feed. Many of the Honda carb assemblies have a diaphragm ON the assembly for controlling gas flow and there must not be a diaphragm in the petcock.

Hey wired, i dunno about that..There is 3 tubes coming off or going in to the petcock, one is a drain/vent, one is vacuum, one is gas feed.The vacuum line goes into the crankcase, and the manual also says its vacuum operated. Now im confused. Again, I didnt have these problems until i switched tanks and threw out that filter.There is no prime, but on, off, res.. The bike is an 82 Honda gl500 silverwing..