Lance Gamma Supplemental Petcock Kit for RZ500

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Rick Lance
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Location: Leicester, NC
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Lance Gamma Supplemental Petcock Kit for RZ500

#1 Post by Rick Lance » Thu Aug 31, 2017 12:37 pm

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.

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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.

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

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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.

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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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FlyingBoat
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Re: Lance Gamma Supplemental Petcock Kit for RZ500

#2 Post by FlyingBoat » Tue Nov 26, 2019 10:58 pm

This looks interesting...

New WaWa station now sells 89 octane ethanol free gas about 60 cent more than regular 87 with ethanol.

Lucky me I’m an aircraft mechanic and have access to 100 octane low lead av gas about 5 bucks a gallon, great stuff that is.
1985 RZ500S Sold
1985 52X/RZV Project

Orlando7
Posts: 51
Joined: Fri Oct 02, 2015 7:44 am
Location: Kissimmee, FL

Re: Lance Gamma Supplemental Petcock Kit for RZ500

#3 Post by Orlando7 » Mon May 31, 2021 2:08 am

Does anybody do these nowadays, are these still available anywhere?
1975 Kawasaki KH250A5
1977 Kawasaki KH400A4
1977 Benelli Sei 750
1981 Yamaha RD350LC
1984 Yamaha RZ350 Kenny Roberts
1985 Yamaha RZ5001986
1986 Suzuki GSXR750 Skoal Bandit

ChequeredFlagRacing
Posts: 336
Joined: Fri Mar 24, 2017 10:08 am
Location: United Kingdom

Re: Lance Gamma Supplemental Petcock Kit for RZ500

#4 Post by ChequeredFlagRacing » Mon May 31, 2021 5:44 am

You could fit the Yamaha TZR250 Fuel Filter / Tap 3MA-24510-00 the tank. Fiddly to get to if you don't lift the tank but it only has on and off and both lines are live when in the on position
https://scontent-lcy1-1.xx.fbcdn.net/v/ ... e=60D85272
Yamaha FS1E 1975
Yamaha RD200 1976
Yamaha RD400 1977
Yamaha AS3 125cc 1978
Yamaha AS1 125cc 1979
Honda CX500
Honda MT125cc 1980
Yamaha TZ125G 1981-82
Zeger TC500cc 1983-84
Yamaha RD500LC 1985-87
Honda C90 1989
Yamaha DT175 1993
Yamaha RZV500R 2018

ChequeredFlagRacing
Posts: 336
Joined: Fri Mar 24, 2017 10:08 am
Location: United Kingdom

Re: Lance Gamma Supplemental Petcock Kit for RZ500

#5 Post by ChequeredFlagRacing » Mon May 31, 2021 5:46 am

Cut the lever down to clear heatshield

https://scontent-lcy1-1.xx.fbcdn.net/v/ ... e=60D9FE76
Yamaha FS1E 1975
Yamaha RD200 1976
Yamaha RD400 1977
Yamaha AS3 125cc 1978
Yamaha AS1 125cc 1979
Honda CX500
Honda MT125cc 1980
Yamaha TZ125G 1981-82
Zeger TC500cc 1983-84
Yamaha RD500LC 1985-87
Honda C90 1989
Yamaha DT175 1993
Yamaha RZV500R 2018

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