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Valkyrie Riders Cruiser Club > General > 1500 Tech Board > Petcock
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Author Topic: Petcock  (Read 1009 times)
grapher
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Posts: 4

LaVernia, Texas
« on: January 27, 2013, 06:20:15 PM »
I had my fuel tank off to repalce some vacuum hoses and while I had the fuel tank off I decided to check the petcock.  It was about half full of gas so I hooked a fuel hose to it and running it to an empty fuel can.  I then hooked a hose attached to a vacuum  pump to the vacuum plug.  When I pumped vacuum applying pressure to the petcock the fuel would flow.  But it would not maintain pressure.  I had to keep pumping to keep pressure in the line.  I know the vacuum pump will hold because I clamped the line  and it maintained pressure.  Is it normal for the petcock to leak down?  Is this a vacuum leak in the system?  I put it back together and it did seem to run okay
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custom1
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Posts: 333


01 Interstate

SW Pa
« Reply #1 on: January 27, 2013, 07:25:59 PM »
It's my understanding that it should hold the vacuum. It will probably run ok until situations that require lots of fuel all at once. Depends how bad the leak is as to how far open the valve is.

There are a lot of posts regarding this subject. Just search "vacuum petcock".

Here is the most recent one.

http://www.valkyrieforum.com/bbs/index.php/topic,51460.0.html
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John
olddog1946
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Posts: 1830


Moses Lake, Wa
« Reply #2 on: January 27, 2013, 07:30:58 PM »
As long as the engine is running you have vacuum at the petcock. I don't know if the petcock will hold a vacuum from a measured amount. As long as it closes off when you release the vacuum and opens when you supply it I would think you are good to go..

Just my thoughts, I could be full of stuffing or something.
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Michvalk
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Posts: 2002


Remus, Mi
« Reply #3 on: January 28, 2013, 05:24:41 AM »
It should hold vacuum. If the bike is running OK, the fact that the vacuum won't hold, is just a precursor of things to come. You need to get the cover set for the petcock, or replace it. The petcock will work great until the most inoppertune time, then you'll walk to get parts. Fix it BEFORE it goes cooldude
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97Valk_CT_Euless
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Posts: 167


Euless Tx
« Reply #4 on: January 28, 2013, 05:33:23 AM »
Should hold vacuum. Mine did exactly the same thing, installed the cover kit and now it holds vacuum. Found the problem first when syncing carbs. Don't have a bag pum so you can imagine how I kept it running...
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Momz
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ABATE, AMA, & MRF rep.
« Reply #5 on: January 28, 2013, 02:16:12 PM »
Did you have the gas cap in the closed/locked position?
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97 Valk bobber, 98 Valk Rat Rod, 2K SuperValk, plus several other classic bikes
grapher
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Posts: 4

LaVernia, Texas
« Reply #6 on: January 29, 2013, 11:45:30 AM »
tried it both ways with the cap closed and locked and open.  Acted the same way both times
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