I just bought a beautiful red ZL600 in perfect shape. A question about the petcock postion, owner's manual says to leave it on but service manual says put in pri. Any idea which it should be? This looks like a great place for me to learn about my ride. Z
leave the petcock in the on position. It is vacuum operated and will only flow gas while the engine is running. You only need to use prime when starting the bike after it has been sitting for some time or maybe after running out of gas so you can fill the float bowls. If you leave it in the prime position you will have gas flow at all times. Not good, if your floats do not hold tight.
golddrakul
Senior Member
Welcome to the site; the petcock is vacuum operated and has 3 positions - on,reserve, and prime. There is no off. There is a vacuum line attached to the back of the petcock that opens it and allows fuel to flow when vacuum is present in either the on or reserve position; the difference between on and reserve being how far down in the tank the inlet tube for the petcock is. Since it doesn't have a gauge, you normally run the bike in the on position, when it starts to sputter from lack of gas, put it on reserve and get to a gas station! Prime bypasses the vacuum control, it's like a faucet dumping gas to the carbs. Its purpose is to provide fuel to the carbs in a situation where the bike has been sitting a while and there isn't any fuel in the carb float bowls; you would set the petcock to prime for a short time to start the bike and then switch to on. You don't want to leave it in the prime position, the carbs on these bikes are finicky and leaving gravity fed fuel pressure on the carbs when the bike is sitting can overcome the float needles in the carbs, flood the engine internally with gas [which can cause a hydraulic lockup and bent rod] and drip gas on the floor. Those are bad things!
Also, leaving it on prime won't give you any reserve fuel if you miscalculate and run out!