Motorcycle Questions? Ask a Mechanic.
Hi, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.Initially, can you please post a clear picture of the petcock? Click HERE.
Also of interest would be the back.
Depending on the version/petcock, it is possible that the vacuum activated valve has an issue; either no or weak vacuum or the vacuum valve itself has failed. This vacuum activated valve is responsible for automatic On/Off of the petcock depending if there is vacuum/engine is running.