testing petcock
 

Is there any way to test to see if the petcock is alowing the proper amount of flow?

There's really no specification on flow. It's either on or off. Hooking up a mighty vac to the line which goes to the nipple on the BACK of the petcock will give you on/off testing. Make sure the petcock is turned on. Use an 8mm wrench and I think fully CCW is on. If you pull the petcock off there is a strainer attached to it. That could be clogged.

I mixed up the attachment on the petcock when re-installing the tank.

After finding and fixing the problem, I tried pulling vacuum on the petcock to sync carbs and it will not hold vacuum. Is it vented or busted?

Try a different hose and make sure connections are tight. If everything seems to be holding and you're still losing vacuum then the diaphragm is busted and you need a new petcock.