Fixed leaking petcock; Don't buy a new one yet!

gzlocal · 12-29-2011, 05:56 PM

*Mods, I'm not sure whether to put this in the How-To or Troubleshooting section. Move where appropriate if needed!*

Hi guys! Being a graduate student I have not been able to contribute as much as I'd like to, but I had finally been presented with the first issue my bike ever had: a leaking fuel petcock. This is a common issue on the GZ, and can present itself many different ways:

1. Leaking underneath the tank at mating surface gasket to petcock.
2. Leaking out the petcock fuel selector switch.
3. Not stopping flow without vacuum and overflowing carburetor due to malfunctioning or misadjusted needle seat.

I was firstly presented with the number two scenario. I searched on here and saw that some people saw that when dirt had worked its way into the switch and caused some minor leaking. When I disassembled my petcock, I did not see any dirt, but it stopped the leak, so I didn't think any more of it.

Well, the time came to adjust my valves, so I removed the tank, and was met with a nice, nearly unrestricted flow of gasoline out of the petcock, even though the engine was not running and it was not set to prime. Luckily, my needle seat was still working so I didn't have a puddle of gasoline waiting for me in the morning. So I figured maybe some dirt had gotten between the o-ring on the vacuum actuated valve and it wasn't closing all the way. Well, when I disassembled the petcock for a second time, I saw how bad a shape the o-ring was really in. It was no longer round, and looked to be mashed at a weird angle on the edge.

So I tried many things, like turning the o-ring around, stretching it, letting it sit overnight to reform its shape, and it still leaked no matter what I tried. This o-ring is a tapered o-ring, and if it gets damaged or mis-shapen, it will leak no matter what you do. Gz rider has a post on this issue already. (Shoutout from Kannapolis Gz rider! :retard: ) He has much better pictures of disassembly. I strongly recommend you to read this before attempting any repairs! Here is the link:

http://www.gz250bike.com/forum/viewt...hp?f=10&t=5281

The o-ring in question is the one pointed to in red. His was actually better off than mine...

Thing is, at least here in K-Nap, is you can't find any tapered o-rings. But when I started thinking about it, I figured it really wouldn't matter whether it was tapered or not as long as you got the right thickness to allow compression, but also for the vacuum of the engine to pull it off when running. So I set to work finding the perfect size o-ring for replacement, as it is much cheaper than $80 for an entirely new petcock all because of a small doughnut of rubber. (More difficult than it sounds, trust me!)

First off, be sure to look at picture four in Gz rider's post. This shows the o-ring location, and the opened up petcock. Be very careful with the diaphragm and internal gaskets. You can't replace those, and they are very fragile! One nick, and it will either leak, or not be able to hold vacuum to actuate the valve and all this will be for nought!

Secondly, you need NITRILE (Buna-N) or VITON o-rings. These are the only materials that will stand up to the gasoline exposure. If you just get regular old unlabeled cheapies, they will disintegrate, and you will be cleaning a black, sticky goo out of your petcock, carb, and possibly your gas tank. Nitriles are cheapest and work just as well as the expensive VITON's, so if you can find them, then use them.

Ok, here we go. The EXACT size you need is as follows: ID=4.8mm OD=8.6mm Thickness=1.9mm
I needed some other o-rings, so I bought a kit for $10 at Harbor Freight. If you have a Harbor freight near you, these are the exact part numbers: Kit item#=67580 Exact o-ring part#=P5 or 008 in the kit. Here's a pic:

Ok, so easy enough, just pull off the old o-ring and replace it with the exact one mentioned above, or if you have the kit, o-ring 008. When you put the petcock back together, you'll notice the two halves of the valve do not sit flush all the way down like before unless you push them together. THIS IS WHAT WE WANT! This was the way it should have been new from the factory, it means that the o-ring is thicker than the worn out original and is making contact with the mating surface without engine vacuum applied, sealing off gas flow.

There are considerations here! NOTE: NOT ALL O-RINGS ARE THE EXACT SAME SIZE! EVEN IN THE SAME BATCH! If it is too thick, the vacuum will not be able to pull it back enough to allow enough fuel to flow. If it is too wide, it won't seal correctly and will still leak. If it's too narrow, it won't seal against the mating surface and will still leak. Test it first! Here's how.

1. Get a hand-held vacuum pump. If you don't have one, no worries (I don't!), but make sure all the gas is out of the petcock, because you'll be putting your mouth on it...
2. Locate the brass fitting on the petcock that goes to the vacuum line on the carb, marked in red in the picture. Suck on it to give it vacuum. You should hear something move inside the valve while you are doing this. This tells you everything inside is still moving and still working, and the diaphragms are ok.

3. After putting it under vacuum, hold that vacuum inside by plugging the fitting with your tongue. Now take your other finger and start tapping on the main fuel outlet that leads to the carburetor bowl on the petcock. This is the fitting you took the fuel line off of (still attached in picture). This will give you a distinctive hollow sound, as access to the yellow tubes that go inside the fuel tank have been opened with vacuum.
4. Now pull off your tongue while still tapping on the main fuel line outlet; you should hear the sound change to a less hollow tone. That means that the o-ring has returned to a resting position in the valve and sealed off flow to the gas tank pick-ups.
5. One last test! Since it is supposedly sealed, attempt to suck on the main fuel line fitting on the petcock (where the fuel line was attached). If you can't get any air to come through, no gas is going to be able to leak through!
6. Mount in tank, turn tank rightside up, and see if any leaks out the petcock. If not, turn the valve to the prime position to see if any starts to flow. If so, turn to reserve position to ensure it stops flowing and is not leaking there either. If not, SUCCESS! Mount on bike and go for a ride. When you shut off the bike, squeeze the fuel line going from the petcock to the carb. You should not hear any bubbling inside the tank after the first squeeze or two, which is symptomatic of gas bubbles being forced up into the tank from the petcock, meaning it isn't sealing.

Here is a pic of the old and new side by side (apologies for my sucky camera!):

This worked for me on the first try, and I have not had any issues. So make sure you get the EXACT size o-ring listed. Also, if yours still leaks and you don't want to spend $80 on a new one, you can get one from a Suzuki LT80 or KFX80 for around $18. It is not vacuum operated, but it has the same mounts and gasket shape and tubes with reserve, so you just mechanically shut off the fuel when parking the bike and plug the vacuum line to the carb. Many people actually prefer this, as they usually don't leak (ever!). Here is an ebay link to those valves should this not work for you if you want to save some money:

http://www.ebay.com/itm/190618010208...9#ht_963wt_952

Hope this helps someone else with this issue/saves them $80!

Regards fellow riders,
-GZlocal

*Update* So a quick update. I've had the o-ring in the petcock for about 2 weeks, and I have had no issues at all. The bike doesn't leak, and doesn't starve for fuel under full throttle, so the o-ring is sealing and unsealing completely normal. I also disassembled the petcock to check the o-ring's shape, and it seems to have a tapering to it now, although not quite as much as the original o-ring had. Which leads me to believe that the o-ring may never have been tapered from the factory, and may very well just do that with age to a point where it will no longer seal correctly.

wacio · 07-08-2016, 01:09 AM

I do have the patcock described in original post as manual alternative (linked on eBay). It wouldn't fit GZ without some modifications. The knob in reserve position will interfere with the tank weld seam. There might be similar petcock with distance from knob to mounting flange larger that is more suitable for GZ as non vacuum operated replacement.

I purchased this one. Not sure if the screws are same distance but gave it shot. Will let you know if it works. It looks like valve it further from mounting flange:
http://www.ebay.com/itm/321479366875...%3AMEBIDX%3AIT

12-29-2011, 05:56 PM	#1
gzlocal Member Join Date: Jul 2011 Location: Kannapolis, NC Posts: 33	Fixed leaking petcock; Don't buy a new one yet! Mods, I'm not sure whether to put this in the How-To or Troubleshooting section. Move where appropriate if needed! Hi guys! Being a graduate student I have not been able to contribute as much as I'd like to, but I had finally been presented with the first issue my bike ever had: a leaking fuel petcock. This is a common issue on the GZ, and can present itself many different ways: 1. Leaking underneath the tank at mating surface gasket to petcock. 2. Leaking out the petcock fuel selector switch. 3. Not stopping flow without vacuum and overflowing carburetor due to malfunctioning or misadjusted needle seat. I was firstly presented with the number two scenario. I searched on here and saw that some people saw that when dirt had worked its way into the switch and caused some minor leaking. When I disassembled my petcock, I did not see any dirt, but it stopped the leak, so I didn't think any more of it. Well, the time came to adjust my valves, so I removed the tank, and was met with a nice, nearly unrestricted flow of gasoline out of the petcock, even though the engine was not running and it was not set to prime. Luckily, my needle seat was still working so I didn't have a puddle of gasoline waiting for me in the morning. So I figured maybe some dirt had gotten between the o-ring on the vacuum actuated valve and it wasn't closing all the way. Well, when I disassembled the petcock for a second time, I saw how bad a shape the o-ring was really in. It was no longer round, and looked to be mashed at a weird angle on the edge. So I tried many things, like turning the o-ring around, stretching it, letting it sit overnight to reform its shape, and it still leaked no matter what I tried. This o-ring is a tapered o-ring, and if it gets damaged or mis-shapen, it will leak no matter what you do. Gz rider has a post on this issue already. (Shoutout from Kannapolis Gz rider! :retard: ) He has much better pictures of disassembly. I strongly recommend you to read this before attempting any repairs! Here is the link: http://www.gz250bike.com/forum/viewt...hp?f=10&t=5281 The o-ring in question is the one pointed to in red. His was actually better off than mine... Thing is, at least here in K-Nap, is you can't find any tapered o-rings. But when I started thinking about it, I figured it really wouldn't matter whether it was tapered or not as long as you got the right thickness to allow compression, but also for the vacuum of the engine to pull it off when running. So I set to work finding the perfect size o-ring for replacement, as it is much cheaper than $80 for an entirely new petcock all because of a small doughnut of rubber. (More difficult than it sounds, trust me!) First off, be sure to look at picture four in Gz rider's post. This shows the o-ring location, and the opened up petcock. Be very careful with the diaphragm and internal gaskets. You can't replace those, and they are very fragile! One nick, and it will either leak, or not be able to hold vacuum to actuate the valve and all this will be for nought! Secondly, you need NITRILE (Buna-N) or VITON o-rings. These are the only materials that will stand up to the gasoline exposure. If you just get regular old unlabeled cheapies, they will disintegrate, and you will be cleaning a black, sticky goo out of your petcock, carb, and possibly your gas tank. Nitriles are cheapest and work just as well as the expensive VITON's, so if you can find them, then use them. Ok, here we go. The EXACT size you need is as follows: ID=4.8mm OD=8.6mm Thickness=1.9mm I needed some other o-rings, so I bought a kit for $10 at Harbor Freight. If you have a Harbor freight near you, these are the exact part numbers: Kit item#=67580 Exact o-ring part#=P5 or 008 in the kit. Here's a pic: Ok, so easy enough, just pull off the old o-ring and replace it with the exact one mentioned above, or if you have the kit, o-ring 008. When you put the petcock back together, you'll notice the two halves of the valve do not sit flush all the way down like before unless you push them together. THIS IS WHAT WE WANT! This was the way it should have been new from the factory, it means that the o-ring is thicker than the worn out original and is making contact with the mating surface without engine vacuum applied, sealing off gas flow. There are considerations here! NOTE: NOT ALL O-RINGS ARE THE EXACT SAME SIZE! EVEN IN THE SAME BATCH! If it is too thick, the vacuum will not be able to pull it back enough to allow enough fuel to flow. If it is too wide, it won't seal correctly and will still leak. If it's too narrow, it won't seal against the mating surface and will still leak. Test it first! Here's how. 1. Get a hand-held vacuum pump. If you don't have one, no worries (I don't!), but make sure all the gas is out of the petcock, because you'll be putting your mouth on it... 2. Locate the brass fitting on the petcock that goes to the vacuum line on the carb, marked in red in the picture. Suck on it to give it vacuum. You should hear something move inside the valve while you are doing this. This tells you everything inside is still moving and still working, and the diaphragms are ok. 3. After putting it under vacuum, hold that vacuum inside by plugging the fitting with your tongue. Now take your other finger and start tapping on the main fuel outlet that leads to the carburetor bowl on the petcock. This is the fitting you took the fuel line off of (still attached in picture). This will give you a distinctive hollow sound, as access to the yellow tubes that go inside the fuel tank have been opened with vacuum. 4. Now pull off your tongue while still tapping on the main fuel line outlet; you should hear the sound change to a less hollow tone. That means that the o-ring has returned to a resting position in the valve and sealed off flow to the gas tank pick-ups. 5. One last test! Since it is supposedly sealed, attempt to suck on the main fuel line fitting on the petcock (where the fuel line was attached). If you can't get any air to come through, no gas is going to be able to leak through! 6. Mount in tank, turn tank rightside up, and see if any leaks out the petcock. If not, turn the valve to the prime position to see if any starts to flow. If so, turn to reserve position to ensure it stops flowing and is not leaking there either. If not, SUCCESS! Mount on bike and go for a ride. When you shut off the bike, squeeze the fuel line going from the petcock to the carb. You should not hear any bubbling inside the tank after the first squeeze or two, which is symptomatic of gas bubbles being forced up into the tank from the petcock, meaning it isn't sealing. Here is a pic of the old and new side by side (apologies for my sucky camera!): This worked for me on the first try, and I have not had any issues. So make sure you get the EXACT size o-ring listed. Also, if yours still leaks and you don't want to spend $80 on a new one, you can get one from a Suzuki LT80 or KFX80 for around $18. It is not vacuum operated, but it has the same mounts and gasket shape and tubes with reserve, so you just mechanically shut off the fuel when parking the bike and plug the vacuum line to the carb. Many people actually prefer this, as they usually don't leak (ever!). Here is an ebay link to those valves should this not work for you if you want to save some money: http://www.ebay.com/itm/190618010208...9#ht_963wt_952 Hope this helps someone else with this issue/saves them $80! Regards fellow riders, -GZlocal Update So a quick update. I've had the o-ring in the petcock for about 2 weeks, and I have had no issues at all. The bike doesn't leak, and doesn't starve for fuel under full throttle, so the o-ring is sealing and unsealing completely normal. I also disassembled the petcock to check the o-ring's shape, and it seems to have a tapering to it now, although not quite as much as the original o-ring had. Which leads me to believe that the o-ring may never have been tapered from the factory, and may very well just do that with age to a point where it will no longer seal correctly. Login or Register to Remove Ads
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07-08-2016, 01:09 AM	#2
wacio Senior Member Join Date: Apr 2016 Location: Illinois Posts: 174	I do have the patcock described in original post as manual alternative (linked on eBay). It wouldn't fit GZ without some modifications. The knob in reserve position will interfere with the tank weld seam. There might be similar petcock with distance from knob to mounting flange larger that is more suitable for GZ as non vacuum operated replacement. I purchased this one. Not sure if the screws are same distance but gave it shot. Will let you know if it works. It looks like valve it further from mounting flange: http://www.ebay.com/itm/321479366875...%3AMEBIDX%3AIT Last edited by wacio; 07-08-2016 at 04:40 PM.
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