How to test a vacuum operated petcock

[arveejay]

This test only applies if your petcock has a lever on it. Performing this test could cause gas to enter the smaller hose and could get gas in your sucking device. There are 2 nipples on a vacuum petcock. The bigger size nipple is for gas and the smaller nipple is for vacuum. With the lever pointing to (run or on, or reserve) there should be no gas coming thru the petcock, with the lever turned to prime gas should flow. If your petcock passes this test proceed with the rest of the test. If it doesn't, the petcock needs replaced. You now attach a hose to the smaller nipple that you will create a vacuum on and a bigger hose from the larger nipple to a gas can or similar vessel. With the lever turned to on or reserve you should suck on the smaller hose and it should create and hold a vacuum in the petcock. If it won't create a vacuum and hold it the petcock is bad. When you suck on the smaller hose it should release gas from the larger nipple and flow freely. When you release the vacuum the gas flow should stop. Do this several times, each time a vacuum is created and released, gas should flow and stop. If this isn't true the petcock is bad. If you get gas from smaller hose or no constant vacuum the petcock is bad. If the petcock fails any of these tests you are at risk of gas flowing into the nipple on the carb that should create the vacuum in the petcock, and directly into your oil and losing the lubrication properties of the oil. Replacement petcocks are available at www.bikebandit.com .

[arveejay]

If your considering rebuilding instead of replacing you should know. The rebuild kits have come with the wrong size seals and have failed. Better off with a new petcock of which you can depend.

[Hooked Up]

Just curious; What commonly "fails" on these units? I'm on my way back up with my '78 GS 1000. I've completely rebuilt my carbs. They only varnish I encountered was on #1 and #2 bowls. The previous owner said he had drained the carbs prior to storage but obviously there was a little left and he used the siestand. I haven't even removed the petcock yet. Should I or should I wait and see? What are the most common symptoms of a bad vacuum petcock? Thanks in advance, Guy

[arveejay]

Just curious; What commonly "fails" on these units? I'm on my way back up with my '78 GS 1000. I've completely rebuilt my carbs. They only varnish I encountered was on #1 and #2 bowls. The previous owner said he had drained the carbs prior to storage but obviously there was a little left and he used the siestand. I haven't even removed the petcock yet. Should I or should I wait and see? What are the most common symptoms of a bad vacuum petcock? Thanks in advance, Guy

What fails is the diaphram in the petcock. Like any rubber item that has sat unused for years, it dries out and becomes brittle, allowing gas to flow through the bad rubber diaphram.
If forgetting to turn off your gas and filling your oil pan with gas doesn't bother you, there's always the option of buying a

[Jethro]

Pingel....

[Hooked Up]

What's a "Pingel" ? Pics? Guy

Pingel....

[Bud Merrill]

pingel is an aftermarket supplier for bikes they do carry a lot of GS stuff, their petcock's are high quality, "pass more gas"

[Hooked Up]

Thanks Bud! found 'em on the web. Just having a little trouble figuring out which setup I need for a '78 Gs 1000. That's a kewell site with a "bunch" of neat stuff! Guy

[arveejay]

For the new guys

[Billy Ricks]

One other thing, if the prime position doesn't get gas flowing you can do something about it in most cases. If you take the portion of the petcock apart where the lever is you will find a rod for want of a better word, with a loop of spring built into it. Be careful because there is a spring to watch for behind the lever. The rod pushes on the diaphram to let fuel flow. Just lengthen that a little with a light tug and reassemble and test the prime position again. It may take a couple of attemts to get it right but it's easy enough. If you go too far the fuel won't shut off.

[uscwks]

Speaking on the subject of fuel

Do any of you gentlemen have a schematic of the fuel and vaccum line placement?

[arveejay]

Do yourself a favor and go to user cp and edit signature to include what bike you are working on. That will get you more model specific info. There are 2 lines on petcock. the line originating from #2 carb is vacuum and goes on the smaller nipple on the petcock. The fuel line originated from between the 2 middle carbs, #2 and #3. goes to the bigger nipple on the petcock.

[copperaxe]

I have a 82 gs450e and i'm wondering about a schematic for the routing.

It seems like there is a fuel pump on the tank with a nipple on it. What attaches to there? 8-[

[copperaxe]

I am stupidly baffled about this because it doesn't make sence that there is a fuel pump that is under the tank on the opposite side of the frame tunnel, but I don't know what it is since I'm also pretty sure it isn't a sending unit????

What connects to this nipple and why???

[arveejay]

I've never had a 450 and am unsure about a fuel pump. Post a question in the technical area and someone with a 450 should answer your question.