Leaking fuel Petcock

  • Oldzeuski
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Leaking fuel Petcock

24 May 2025 14:07
#912818
My kz650 was leaking fuel so I pulled the petcock and ordered a rebuild kit. When I installed the kit I noticed a few things that don’t make sense. 

First of all, the fuel selector lever is not held firmly against the rubber seal behind it. It appears the plate with fuel markings is meant to hold this in place, but it actually allows the lever to be pulled out just enough that the rubber seal behind it isn’t able to properly seal. It’s almost like the seal is .030 too thin. But I put the original back in and it still had this issue. Very Strange. 

Second, after installing the petcock with all new parts, it still leaked. I was able to verify this is due to the internal spring not pressing enough on the diaphragm. The fuel was leaking by the o ring as it should when vacuum is applied and the diaphragm compresses the spring, even tho there was no vacuum.

The spring is installed correctly, but on a bench set up I was only able to stop the flow by using my thumb and putting force on the diaphragm while the cover was removed. Far more force than the spring can exert. 

I even went back to the original o ring and diaphragm, thinking maybe the rebuild was junk and too large or small and wasn’t fitting correctly to make a good seal. Same problem. 

honestly I’m amazed it didn’t always leak, but it worked fine until this season. 

I bought a new OEM unit to replace this one. But I’m just curious if anyone knows why this one is leaking. 

the pictures are the petcock. The one with the fuel lever off is showing the rubber seal. 
 

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  • TexasKZ
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Re: Leaking fuel Petcock

24 May 2025 21:51 - 24 May 2025 21:54
#912827
Did you polish the seating area that the oring is supposed to seal against? If there is any pitting or roughness in the surface, the oring will not seal well.

Also, there should be a spring washer between the retaining plate and the selector lever that forces the lever against the oring.

www.partzilla.com/catalog/kawasaki/motor...uel-tank-81-82-h1-h2
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24
Last edit: 24 May 2025 21:54 by TexasKZ.
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  • Oldzeuski
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Re: Leaking fuel Petcock

25 May 2025 08:30
#912840
Well the spring washer was missing apparently. It didn’t have one when I pulled the petcock apart tho so how it never leaked before is a mystery. 

I’ll try polishing the o ring surface and see what happens. I’ve got a new petcock coming either way so this is just going to be a backup I suppose. 

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  • ckahleer
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Re: Leaking fuel Petcock

26 May 2025 18:54
#912894
Search "wave spring washer" on E-bay. They come in all sizes.
1997 ZL600
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Re: Leaking fuel Petcock

02 Jun 2025 07:53
#913239
Thank you. If the new one is also missing this washer I will order a replacement. 

I polished the interior hole where the diaphragm and o ring are supposed to fit into. The o ring still does not fit. I’m guessing it never actually sealed and only recently began leaking severely enough that I was able to see the puddle of gas before it evaporated. Probably from ethanol deteriorating the rubber. 

I may end up adding an inline cutoff so this can’t ever happen again. 

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  • TexasKZ
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Re: Leaking fuel Petcock

04 Jun 2025 17:50
#913369
If the oring does not fit, perhaps it is the wrong one.
1982 KZ1000 LTD parts donor
1981 KZ1000 LTD awaiting resurrection
2000 ZRX1100 not ridden enough

www.kzrider.com/11-projects/620336-anoth...uild-thread?start=24

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  • asphalt900
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Re: Leaking fuel Petcock

05 Jun 2025 03:38
#913378
These diaphragm petcocks can be a hassle. Look closely, i mean REALLY close at the "cone" sector where the diaphragm protrusion with o-ring resides. Should be a machine like finish with NO scratches/burrs. Buying a "kit" can sometimes cause false hope. Try a #007 oring, that's generally what they require. I do a lot of the Kawasaki H1-H2 series petcocks and they use the same.  
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  • ThatGPzGuy
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Re: Leaking fuel Petcock

05 Jun 2025 05:32
#913381
All of my bikes have their original petcocks. They can be made to work without leaking. I've posted this before, but this is the tutorial I usually reference. It's for a Yamaha but they are very similar to Kawasaki petcocks. 
Rebuilding Yamaha Petcocks
Jim
North GA
2016 Yamaha FJR1300ES
1982 GPz750 R1
1974 Kawasaki H1
1976 Kawasaki KZ400
1979 Yamaha XS650 cafe'
2001 KZ1000P
2001 Yamaha YZ426
1981 Honda XR200 stroked in an '89 CR125 chassis
1965 Mustang
1967 Triumph GT6
1976 Bronco
"If you didn't build it, it's not really yours"
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