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 Post subject: Lance Gamma Supplemental Petcock Kit for RZ500
PostPosted: Thu Aug 31, 2017 12:37 pm 
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Joined: Thu Nov 17, 2005 11:12 am
Posts: 371
Location: Leicester, NC
From Luther in OK-

The problem I had was with the vacuum valve on the backside of the petcock. Take the cover off and there is a shaft with an O ring and a spring holding it closed. It doesn't seal worth a damn and gives a constant supply of fuel 24 hours a day. If you also have a bad float needle and seat in one of the carbs expect to find a pool of gas or a burned down house when you come home.
What I did was push the shaft with O ring past the tapered seat into the petcock with my thumb till it bottomed out. The vacuum valve is now disabled and won't leak. Put the spring and cover back on. On the front of the petcock take the 2 screws, wave washer and selector lever out and reassemble them rotated 180 degrees. Now it should have on, off and reserve. It also flows a whole lot more fuel.

My irritation with the stock petcock configuration is that the fuel ALWAYS flows whenever the motor is running. That means that if you ever have a hung or stuck float (a common experience for me brought on by fuel quality or contaminants), there's no way to keep the motor running while shutting off the petcock. If this were possible, oftentimes the problem will clear itself. Instead, with the stock setup, if you were to attempt to keep it running, the stuck float would continue to gush fuel until the plug fouls or the bike burst into flames. The purpose of my Supplemental Petcock Kit is to give a positive fuel shutoff option while performing the Luther mod takes care of the always on issue very nicely. The stock petcock is used to maintain the ON/RES/OFF function while the SP assures a positive interruption of fuel when desired. I have not had much luck with 30 year old petcock designs when addressing modern fuels. Even new petcocks for the Gamma and RZ5 leak within weeks in my garage. Since I have a dozen 500's sitting around at any given time, positive fuel shutoff is absolutely mandatory in my shop. The SP is constructed with a brass body, a stainless steel ball and a Teflon seat so it is impervious to today's fuels. The routing for my SP kit requires the Luther mod to invert the handle. Here's how it's done:

Dismantle the petcock by removing the 5 screws from the diaphragm side to expose the plunger.


Press the plunger into the petcock body until it sticks in place. I do this with a small socket and a bench vise but you can improvise. Once the valve is stuck in place re-assemble that side of the petcock.



Then reconfigure the selector lever and retainer plate upside down so that ON becomes straight up.


Remember to cap off both ends of the now by-passed vacuum feed (one on the carb and one on the petcock). You now have a petcock that does not require vacuum and has a position for OFF rather than PRIME. Before you install the petcock, test each position to identify what does what. I find it useful to use Sil-Glyde to lube the petcock gasket for smooth action and include it in my kit.

The end result is that you now can turn your fuel off while the motor is running. The flow rate is not affected adversely and you now have a petcock that is compatible with my supplemental petcock system which offers a leak proof method of fuel control. Email Rick@LanceGamma.com for more info.


If I disagree with everyone, that doesn't make me right. If I take the side of only one, it doesn't end the fight. If my position's strong enough from exposure to the light, you may see things my way when we share the same highway.

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