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What are my Petcock replacement options?

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What are my Petcock replacement options?

PostAuthor: TrailKlaus » Sun Sep 01, 2019 10:22 pm

I'm working on a '83 XV500 Virago at the moment, and I'm struggling to control/eliminate the leaking from the original petcock, with the gaskets and seals being in poor shape. I'm interested in just putting this one behind me and moving to something a bit newer, such as this petcock: ... B07Q6KJ9VF

I've confirmed that the mounting holes match, at 50mm apart. However, I'm uncertain if the ports will sync up between the two that the replacement has, one each for vacuum and fuel, and the three that can be found on the original. Included below is an image of an original, with the three valves labeled. Would someone be able to tell me the purpose for each valve? I believe C is the main fuel line, and B is the vacuum line, but I'm not sure what purpose A serves.

1983-Genuine-Yamaha-Virago-XV500-XV-500-OEM copy.jpg

Ultimately, I'm just trying to find a replacement that is generally compatible with the bike, thus avoiding any unnecessary headache.

Much thanks!
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Re: What are my Petcock replacement options?

PostAuthor: bstig60 » Thu Sep 05, 2019 12:19 pm

Here's the stock replacement for the bike. Take the part number and do a google search. ... a9fe76be80
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Re: What are my Petcock replacement options?

PostAuthor: baxterj787 » Wed Sep 11, 2019 11:07 am

"A" in your picture is the return line. "C" is the line from the tank to the fuel pump. "B" is a small-diameter vac line going to the front intake manifold.

The hexagonal-shaped component in-line between the petcock and carb is the vacuum-operated fuel pump. The pump moves fuel according to engine RPM and is operated off a medium-diameter vac line going to the rear intake manifold; more RPM = more pulses on the fuel pump diaphragm = more fuel moved to the carbs. Why did Y do this? The fuel outlet is lower than the float level in the carbs; a pump is required.

Once the carbs are full and the float has closed, the excess fuel is returned to the tank through that "A" fitting.

Sadly, I have not seen a direct replacement for the petcock on the XV500s. No one makes a rebuild kit either (to my knowledge). This is a case where you have to take the plunge on the part. Thankfully they are still available; remarkable as this valve was only used on the XV500 and XZ Vision 550 for a very short time in the early '80s.
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Re: What are my Petcock replacement options?

PostAuthor: Alvega » Tue May 12, 2020 4:55 pm

I am sorry about the silly question but if there is a fuel pump why the petcock has that diaphragam?

With a "normal" fuel petcock connected to the pump, it wouldnt work?

Thanks :bg:
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Re: What are my Petcock replacement options?

PostAuthor: rchawaii » Wed May 13, 2020 9:19 am

It is a manual pump operated by vacuum which is why the diaphragm. A "Normal" (Non xv500) petcock typically doesnt have a hose to draw vacuum. Not to say one would not work, But so far although I have heard people say to use a "normal" petcock (which requires an adapter plate modified to fit because the holes on the xv500 are 50mm), I have not seen one person describe in detail changing the 500 tank into a regular petcock and it working.

I'm not saying it has not been done. People have said it has, but I haven't seen one yet unless it was modified to a single carb design.

If anyone has proof otherwise, they should post those details.
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Re: What are my Petcock replacement options?

PostAuthor: Peter-Jan » Fri Jun 12, 2020 7:22 am

my petcock was leaking trough the vacuum operating line, that poored fuel directly into the adapter on the front cilinder and that was the reason the front cylinder didn't fire any more. The vacuum membrane was torn and there are no maintanance sets with those membranes available . The petcock spare is too expensive so here is what I did;

I took the whole membranes out. on the front and on the back.
Closed the front with a 0,5 mm sheet gasket. (petrol resistant)
On the back I also closed the the petcock with one 0,5 mm sheet gasket and covering 2 circuits;
1 --> return fuel circuit, if you just close it the fuel is returned as Original into the tank.
2 --> fuel supply circuit, There I made a hole in the middle and used the Original piston + spring to close the hole in the middle.
I took the little notch out of the ring in front of the operating "Rotary knob" on the front of the petcock. In this way the "knob" can turn 360 degrees and this gives 4 operating positions: open, close, reserve, close.

In addition to this you need to add a checkvalve in the return line of the fuel to avoid that the tank is running empty through the carburator "vent"connection.

works fine for me, no new petcock needed. :cl:

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