Rebuilding the petcock/fuel tap

Have any of these happened to you?

• You notice your gas is disappearing.
• You notice that your oil level is getting higher, but you haven't been adding any oil.
• You walk by your bike and smell gas.
• Your petcock is very hard to turn.
• You have gas leaking from your petcock (the obvious one).

This likely means you need to rebuild your petcock. There are several options for doing this:

• Buy a new one, part #51023-1393 – about $65 at Ron Ayers
• Get a used one from eBay or one of the usual sources
• Get the parts and rebuild it yourself

Obtaining parts

What you decide to do will likely depend on whether you can diagnose which part of the petcock is damaged. This will, of course, involve taking it apart and looking at it before you order parts. This is the cheapest way, but you'll have to wait for parts.

There is a rebuild kit from K&L Supply, part #18-2723, but it is for the E series (86-87) bikes. It doesn't have the correct diaphragm for the later F (88-07) bikes. All the other parts are the right ones, but if your diaphragm is bad, plan on spending another $25 on top of the $25 for this kit, which puts you in the ballpark for a new one, already put together.

K&L Supply part #s:

• 86-87 rebuild kit: #18-2723
• 88-07 diaphragm only: #18-6638

You can get the rebuild kit from Dark Horse Motorcycle Parts or their eBay site, or you can call K&L and find out where your nearest dealer is.

If you want to order the parts separately, here is what you'll need:

• SPRING,TAP DIAPHRAGM- 92081-1240
• DIAPHRAGM,TAP- 43028-1068
• RING-O- 92055-1664
• PACKING- 43049-1103
• RING-O,TAP LEVER- 92055-1085
• RING,TAP FLANGED- 51039-003

Checking the vent

For the diaphragm to work properly, there is a small vent hole to atmosphere on the bottom side of the petcock. This has to be clear. After you disassemble the petcock, check for crud on both sides of the diaphragm. If you're very fortunate, this may be all that is wrong. If there is debris on the fuel side, then a check of the complete fuel system would be prudent.

Rebuild process

The rebuild is pretty straightforward. Drain the tank and remove it. Then take the petcock off the tank.

Remove the 5 screws on the back side. Be careful when you open it, since there is a small spring inside.

The diaphragm has two flaps and goes through the plastic spacer. If you are not going to replace it, just leave it alone. You can take it out of the plastic spacer, but be careful when you do. Take note of the small hump on the plastic piece so you put it back together the right way. Notice how the pointed part is not even on both sides.

Remove the o-ring from the new diaphragm and swap it with the one on yours, or replace it with a new one if you didn't buy a kit.

Remove the two screws on the lever side and take the face plate off. There is a pressure fit washer between the face and the lever body. It's supposed to be wavy; don't try to straighten it out.

The lever body pulls straight out. You might feel some resistance, since there is an o-ring on it. Once you have it out, take the o-ring off.

Remove the black lever gasket (has 4 holes – called 'packing' in the parts diagrams). This is usually one of the first things to cause leaky petcocks. You can buy it by itself for roughly $3, but if you're going to take the whole thing apart you might as well replace the other o-rings, too.

This one was a little chewed on.

Now that you have all the pieces off, take some carb cleaner and a small brush and clean everything. This one had some buildup on the side where the small o-ring on the diaphragm meets the petcock. Don't be too harsh when cleaning. Let the cleaner do most of the work.

Make sure everything is nice and clean. Replace the o-rings on the diaphragm and lever body, then reassemble. You should now have a clean, leak-free petcock. The kit comes with a new o-ring for the petcock-to-gas tank connection as well.

You should probably change your oil now, before you start it up. If the petcock has been leaking into the oil, not only will you have too much oil, what's in there will be thinned out and much less effective. You don't want to replace major engine components just because of that.