Question about 1981 Yamaha XJ 650
The petcock on these bikes is vacuum operated, which means that there are two hoses that go to it. The thicker hose is the fuel line and it runs from the thick port on the petcock to the fuel input on the carburetor rack. The fuel input on the carburetors is located between the number two and number three carburetor bodies. If you aren't sure which is the fuel connection, just turn the petcock switch to prime for a second and you will see gas come out of the fuel connection.
The thinner hose on the petcock is a vacuum line. It runs from the vacuum port on the #3 cylinder (between the carburetor body and the engine) up to the smaller connection on your petcock. When the engine is turning vacuum is applied to this thinner line and allows fuel to run from the tank into the carburetors.
There are the only two lines that should run to your petcock, and the fuel line should not be split anywhere between the petcock and the carburetors.
Posted on Mar 13, 2011
Testimonial: "Thank you for the feedback, It was very helpful. I had been told that both ports on the intake were to be plugged, which added to my confusion, Ted"
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