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Stupid petcock question

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Here's my stupid petcock question. My green DRZ-S (2003 KLX400SR, stock Mikuni CV carb) has a petcock with 3 positions - ON, PRI, and RES. There is no "off". There is a vacuum line, which is supposed to shut off the fuel, right? But when I removed the gas tank for the first time and disconnected the fuel line, fuel poured out of the tank like it came out of a fire hydrant, and didn't stop until the tank was drained. It did not matter what position the petcock was in, nor whether the vacuum line was connected.

Is this normal? :applause: I thought the vacuum line should shut off the gas. Do I have to replace the petcock? If I run it as is, will I fill the cylinder with gas? Or is this why the bike only idles, but dies when I twist the throttle?

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Your experience is typical among those of us who have or had the S petcock. Many of us switched to an E petcock or one off a Yamaha because of the same problems you're having.

Take a look at this: http://www.thumpertalk.com/forum/showthread.php?t=451280. However, there seems to be a problem with using this petcock with the S metal tank.

The Pingle petcock is a very good product from what I've heard and seen.

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In answer to your question -- no, it's not normal.

Without vacuum, it should just dribble a little fuel out from the line, and none from the tank.

Unless it's on Prime, I think.. I don't intend to try that.

Mine is an SM, and I've come to appreciate the stock petcock.

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your petcock does not have an off position.it does have a vent tube on the underside of tank.vaccume or not, id assume with it having a vent tube and then taking off the fuel line to carb sense tells me it(gas) will pour out.

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All vacumn fuel taps (Oz lingo) work under the same principle, on & reserve are the same on any fuel tap vacumn or not, the prime fuction is to prime the carby float bowl after mtce or to flush out water etc out of the carb float bowl. They should not leak fuel in the on & reserve poitions, if they do than the diaphragm in your fuel tap is either stuck open or damaged & needs to be replaced, or alternately change out the fuel tap for a aftermarket one & blank off your vacumn line from carb/intake manifold.

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plus one for pingle. i replaced my stocker after i had the same problem. the pingle isn't cheap, but neither is OEM. plus they are totally rebuildable.

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All vacumn fuel taps (Oz lingo) work under the same principle, on & reserve are the same on any fuel tap vacumn or not, the prime fuction is to prime the carby float bowl after mtce or to flush out water etc out of the carb float bowl. They should not leak fuel in the on & reserve poitions, if they do than the diaphragm in your fuel tap is either stuck open or damaged & needs to be replaced, or alternately change out the fuel tap for a aftermarket one & blank off your vacumn line from carb/intake manifold.

nice first post

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When working properly...

ON and RES = OFF without vacuum pressure

PRIME = ON without vacuum pressure.

:applause:

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I'm going to chime in here, not with direct experience with this particular petcock (I've got an E type), but I did have to rebuild the vacuum petcock on my Virago a couple of summers ago and surely the systems aren't that much different. If I remember correctly, in the RUN and RES positions there is a spring behind the vacuum diaphram that closes off the fuel flow when the engine is dead - vacuum from the running engine overcomes this spring when the engine is, ahem, running, and allows the fuel to flow.:applause: The PRI (prime) position bypasses this blocked path and allows the fuel to flow freely, whether the engine is running or not. The fuel will also keep flowing if the diaphram is rupured or otherwise mangled. I believe this is what you will find when you split the petcock. What you essentially have at the moment is a petcock acting as if it is in the PRI position, which will eventually overload the float valve in the carb and flood the engine (at best) or cause hydraulic lock (at worse). Best to fix it ASAP.

That's what I found in my Virago's petcock. In my case, the diaphram was age-split and allowed fuel past whatever the position. However, the only way I noticed a problem was because the fuel was leaking out the petcock and dripping onto the engine. I was able to find a dealer that knew of a rebuild kit for that particular petcock, so $16 took care of the problem.

I didn't have much luck finding a rebuild kit from the local dealer when my E petcock developed a leak. However, I did find one at a local motorcycle parts/accessory store.

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Thanks for all the advice. I took apart the petcock, blew off some plastic shavings (that seem to be standard equipment with Clarke tanks), and cleaned the vacuum diaphram. It was not torn, probably not seated, or the spring didn't push it back, or some crud kept it open. I put the petcock back together, and now it does not flow gas until there is some vacuum.

I hope it's fixed. Maybe I'll buy the infamous 2GU-24500-02 petcock. It's horizontal output will probably fit better with my 3.9 gal Clarke tank.

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