petcock positions?

I'm new to the xj bikes and was just curious about the positions of the petcock. I'm pretty sure "ON" or "RES" while riding. Is it ok to leave "ON" while parked or should it go to "PRI"? What is "PRI" for anyway? Starting? Thank you all for info.

ck

 

Fuel will only flow with the valve to ON or RES if the bike is running. Set at PRI fuel can always flow.

ON is used for normal operation. RES(erve) is used to get tha last couple quarts of fuel when the tank is running low. PRI(me) is used to fill the carburetor float bowls when they have been drained for some reason.

Because the fuel system is gravity feed any leak-by of the float valves will result in the crankcase filling with gasoline and then spilling of the gasoline on the floor. As a safety the fuel valve assembly has an extra vacuum operated valve that only lets gasoline flow when there is engine vacuum. The PRI position bypasses the safety device.

Summary: Never leave on PRI. Use only to initially fill dry carburetors.

 

Thanks for the info.

ck