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Petcock's , Vacuum "PRI" same as Manual "ON" ???


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So I read in my DRZ400S manual that if you run the engine with the petcock in "PRI" that you could damage the engine. How is running in "PRI" any different than running a manual petcock in the "ON" position? All of my other motorcycles and ATV's have only had manual petcocks that when put to the "ON" position allowed continues flow of gas.

So what is the deal?

Thanks

Greebe

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Thanks for the link, but I did not see any reference towards the "PRI" vs using a manual petcock on the ON position. Or how the "PRI" would damage your engine.

Thanks

Greebe

When in PRI or the petcock is leaking in the on position and the bike is off, fuel can pass the needle and seat to fill the cylinder with fuel and could cause hydrolock or contaminate the oil.

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Thanks for the link, but I did not see any reference towards the "PRI" vs using a manual petcock on the ON position. Or how the "PRI" would damage your engine.

Thanks

Greebe

Agreed, the manual is not clear at all. Your bike has a vacuum petcock. When it's "ON", fuel only flows when the engine is running. When the petcock is set to "PRI", fuel always flows and is only limited by the float valve, which can leak and flood your engine, break down crankcase oil etc, etc.

I guess Suzuki doesn't want to admit that their float valves could leak 🙂

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So if you're removing your tank from the bike, does that mean you want to leave the petcock in the "ON" position?

Sorry, the petcocks on other bikes I've had have had an "OFF" position for removing the tank so I'm a little confused.

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Last year I rode my DRZ from Cincinnati to Prudhoe Bay.My third morning in Edmonton,Ab my bike wouldn't start.Half a day later,I found my vacuum valve was leaking and my needle valve was leaking (the needle valve was good,but the oring was leaking).I don't know why the overflow tube didn't let the gas just run to the ground.But it went into the cyclinder and hydraulicly locked.I thought it was a bad battery for a while.Anyway,when I stopped,I would pull the gas line and plug it.Eventually,I got a manual shutoff valve.

Pri= gas on

on= gas on if there is enough vacuum to open the vacuum valve(and the valve is good)

If the diaphragm is bad (like mine was),the gas will leak through.Mine also leaked into the vacuum line.

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Right now I am doing the same thing. After a ride I pull off the fuel line and plug it. I was going to order on of these right now to put in between the petcock and carb.

amazon_B0038U3JIO.jpg

For about $6 you can get one of these and it should be a cheap simple trick to fixing the problem.

Greebe

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Right now I am doing the same thing. After a ride I pull off the fuel line and plug it. I was going to order on of these right now to put in between the petcock and carb.

amazon_B0038U3JIO.jpg

For about $6 you can get one of these and it should be a cheap simple trick to fixing the problem.

Greebe

Looks identical to the one I installed.And it is fine (like all older bikes),as long as you remember to turn it off.And you don't need to turn it off as long as your float valve is working properly.But if it doesn't....................

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Its not an overflow, its a vent.

Vents are for air.Overflows for liquids.And I really don't know what path the gas was taking.During the next 8000 miles of my trip,I forgot to turn my manual valve off a few times.Depending on how long it sat leaking through,I might have to pull my 4 gallon Clarke tank off to access the spark plug to purge gas from the cylinder.Sometimes there was gas on the ground (overflow).Other times there wasn't.I feel confident that the problem was caused by some bad gas formulation that attacked the diaphragm.The diaphragm material was separating.

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