I found a rebuild kit for the one-year-only 87 GL1200 fuel petcock that works!!!
It's installed on my '87 GL1200 and is working and not leaking!
In case you don't already know, the 87 GL1200 petcock is a one-year-only petcock that was not put on any other Honda motorcycle. It is no longer available from Honda nor is there a rebuild kit for it that fits... until now!
Some history on the issue: The 1987 fuel petcock (PN 16950-ML8-601) is a different part than the fuel petcock (PN 16950-MG9-005) for a 1984, 1985, or 1986 GL1200. The fuel outlet on the 1987 petcock is 3/8" (10mm fuel hose), while the fuel outlet on the 84, 85, 86 is 1/4" (5.5mm fuel hose). The distance between the mounting screw holes is different: the 1987 petcock mounting holes are approximately 46mm apart,while the 84, 85, 86 petcock mounting holes are about 42mm apart. So they won't mount on an '87 fuel tank and vice-versa. The entire body of the 1987 fuel petcock is larger than an 84, 85, 86 fuel petcock. The 1987 petcock body diameter is 32mm. The 84, 85, 86 petcock body diameter is 28mm. The 4-hole gasket (PN 16955-268-020) that comes in a rebuild kit for the 84, 85, 86 fuel petcock is only 20mm in diameter... way too small for the 87 petcock, and the fuel transfer holes in it are too small as well.
I did some research and found out that there is a fuel petcock rebuild kit for some Honda ATVs that fits the 87 GL1200 fuel petcock and can be used to rebuild it.
The fuel petcock rebuild kit that works is for 1986-1989 TRX350 and 1989-1990 FL400R ATVs. The kits are made by Mikuni (the carburetor manufacturers) and they are available on eBay from various sellers. Here's the seller that I bought mine from:
Here are some pictures of the kit contents and the gasket installed in the petcock body.
The first picture shows the contents of the ATV petcock rebuild kit.
The second picture shows original 87 petcock gasket and the replacement petcock gasket that comes with the ATV petcock kit. As you can see, the OD of the original gasket (on the left) is slightly larger than the replacement gasket (on the right). But, the 4 holes are exactly the same size and the same distance apart, so it fits perfectly inside the petcock body.
The third picture shows the original 87 GL1200 gasket in the petcock body.
The fourth picture shows the ATV replacement gasket installed in the 87 GL1200 petcock body.
As you can see, it fits right on the four holes. It doesn't extend to the full ID of the petcock body, but it doesn't need to. It is held very firmly in place by the raised edges around the four hole towers in the body, and the sealing surfaces line up perfectly with the sealing surfaces on the bottom of the top piece of the valve body (the part with the lever on it that you use to turn the valve on and off).
So, you now have a kit you can use to rebuild your leaky 87 GL1200 fuel petcock!
NOTE: The 87 GL1200 fuel petcock was not meant to be rebuilt and is assembled with rivets not screws. So, yes, you have to drill out the rivets that hold the fuel petcock together to get it apart and then drill and tap the holes for the screws that come with the kit, but that is not that hard to do.
What do I win!