Where should the knob be on a petcock on a 1982 Yamaha XJ750 Maxim?

T

T L

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On the petcock when the knob is up it is in RES. When turned to the right it says PRI. Straight down is in ON. Does PRI stand for primary or prime? I have heard that if left in the wrong position gas could flow freely even when off and cause damage.
Thanks km9cm2e for the answer, but which would be the off position? I only have RES, PRI and ON
 
You have a vacuum operated petcock. On and reserve are the vacuum functions and shut off automatically when the engine stops. "pri" means prime and will allow fuel to flow until the tank is dry (engine on or off). Run the bike in the "on "position for normal use, "reserve" is an emergency backup, and "pri" is for refilling the fuel system after draining/removing the tank. Good luck.
 
The rule for petcocks is; If the selector lever is perpendicular to the fuel line it is off, and if the lever is in line with the fuel line it is on. Regardless of what PRI means. If you want to be certain, disconnect the line and see if it runs into a can.
 
You have a vacuum operated petcock. On and reserve are the vacuum functions and shut off automatically when the engine stops. "pri" means prime and will allow fuel to flow until the tank is dry (engine on or off). Run the bike in the "on "position for normal use, "reserve" is an emergency backup, and "pri" is for refilling the fuel system after draining/removing the tank. Good luck.
 
It stands for primary. On modern bikes, it's OK to leave it in this position, because it won't leak. On older bikes such as yours, it should be left OFF when not riding. It's not so much it'll damage anything, but you could drain the tank.
 
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