A leaking fuel valve can be caused by long term storage.
<13px verdana="" geneva="" arial="" helvetica="" sans-serif="">Store any motorcycle or ATV long enough & you will end up with a leaking fuel valve. Could be a drip. Could be more. So you buy a used one off the shelf at a salvage yard. Install it on your bike and it leaks too.
<13px verdana="" geneva="" arial="" helvetica="" sans-serif="">When bikes or quads are dismantled for storage the fluids must be drained from the tanks, carbs, etc. Not only for safety, but because old fuel breaks down and can gum up the moving parts. Mechanics will tell you that it turns to shellac. Probably not quite accurate, but anyone who has stored their snow blower for a year or two and had to clean the carb to use it, knows what I mean.13px>
So the bike has been taken apart and the petcock (fuel or gas valve) sits on a shelf for a few years until it is sold. You buy it, take off your old, leaking fuel valve and install the "new" one and it immediately starts to drip. Now you're mad. The shop must have sold you a defective petcock. Right? Probably not.
When fuel valves are removed from the tank or the tank they are on is drained, the rubber o-rings that are supposed to prevent leaks are exposed to air. This causes them to dry out and shrink. Also, if the valve housing is made of aluminum is will oxidize in the presence of air (oxygen) and can cause a "crust" to form. If this crust is thick enough and in contact with the rubber o-ring it can ruin the seal.
What to do
<13px verdana="" geneva="" arial="" helvetica="" sans-serif="">Before you go back to the salvage yard, screaming that they sell crappy parts, you can do a little homework. The o-ring probably needs to be rehydrated. 13px>
First, if you have a vacuum type valve you need to plug the vacuum port. Take a small piece of vacuum line and push it on to the port. Next, epoxy a bolt into the other end of the line. This will prevent gas from getting in to that side.
Now, take the entire petcock and soak it in gas for 24 hours. Just put it in a coffee can, fill it with gas, put the lid on and leave it alone. When the 24 hours is up, try installing it again. Most of the time, this is all you need to do & it will no longer leak.
If you still have a dripper, you need to remove the screws (bolts) and take it apart. No screws? See below under "Still Leaking?".
Remove the o-ring (rubber seal & diaphragm for vacuum operated valves) and put in some gas and use a stiff plastic bristle brush to clean the groove the o-ring sits in and all surfaces and replace the rubber parts.
If any crust is sticking to the o-ring try rubbing it off with your finger. If you scratch it up with the brush, it will leak anyway. Reassemble the valve and try it again. In most cases, the leak will have stopped and you will be good to go.
Fuel Valve Still Leaking?
<13px verdana="" geneva="" arial="" helvetica="" sans-serif="">If you still have a leaking fuel valve because the rubber o-ring is dry rotted or torn you can try to find a new oem valve, an aftermarket replacement valve or rebuild it yourself.13px>
There are lots of different styles of petcock, but I would say that 90% of them are rebuildable. See page Rebuilding Your Fuel Petcock.
If you have the kind that you cannot access the washer or o-ring, because that valve is riveted together, yours is not rebuildable. Other motorcycle resources may recommend drilling out the rivets that hold it together to get to the washer. Replacing it & reassembling the valve with self-tappers or epoxy.
If you have to go to those lengths, just to repair a leaking fuel valve, I would just buy a replacement.
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