By MarcG: So when not in use petcock should be in what position?
ON is the normal petcock setting:
When the engine is running, engine vacuum actuates a spring-loaded diaphragm to allow fuel to flow by gravity.
Then when the engine is stopped, the spring returns the diaphragm to the closed position, stopping the flow of fuel.
The diaphragm has a plunger w o-ring that plugs an orifice.
RES = reserve.
Functions the same as ON, but the res pickup tube is shorter to use up the remaining fuel in the tank. (about a 1/2 gallon)
Switch to RES when the fuel light comes on or when the fuel gets low. Then refill the tank asap or within 10-20 miles.
PRI = prime. PRI bypasses the diaphragm assy, allowing fuel to flow by gravity whether the engine is stopped or running.
Use prime to prime the carburetors in case the fuel level in the carb bowls is low for whatever reason, such as evaporation.
You can also use prime when draining the carburetors, such as when the fuel is old from not riding in a while.
