In the last 14 months I’ve had three petcocks on my bike. The original CJ one has the American gas eat the seal and then I was able to get a Donghai petcock from Marcus. This would work well on a flathead I believe but does not flow well enough for my OHV at extended high speeds. I would be cruising at over 100 KPH for a while and the bike would act like it was running out of fuel. A quick look down at my clear fuel filters showed them empty. If I slowed down to 90 KPH she would go back to running fine and the filters would fill back up.

First remember there are two basic types of CJ petcock, as Clay calls them innies and outies. Some innies have a bung that actually accepts American pipe thread of maybe ¼ inch NPT or close enough to work. I think Dan fitted a hardware store tap on one of his bikes. Others such as the tank I have use a 14 mm thread that seems quite tough to find a petcock for. After a fair bit of research in all the catalogs at my friend Doug’s bike shop I gave up on finding one.

On a standard outie a Honda 500 petcock fits and there are articles in the toolbox on this. If your bike has the bung extend out of the tank you have an outie. Just a hole means you have an innie.

On the 14 mm innie like mine a Donghai will fit if you can find one and screw right on.

After measuring I decided there was room to drill out and tap the tank bung for 3/8 NPT which is the size Harley uses and there are dozens of petcocks available for.

I used a Harley replacement 90 degree petcock from Drag Specialties pert number DS390217 which is nice quality and cost me about $15 at Doug’s shop.

You will also need a 3/8 NPT tap, a 37/64 drill bit, and I had to buy a ½ inch drill because I couldn’t find a stepped down bit for my 3/8 drill. I also ended up buying a 3/8 NPT die but more on that later.

First follow the directions for removing the fuel tank.

Remember all those welding on gas tank jokes and you don’t want to be the lead story on next year’s Darwin awards. After draining carefully I washed the tank several times and drilled the hole to 37/64 with water running out. I also used a drill with plastic case and checked the ground first. Use all possible precautions.

Then comes the tapping, I have rarely tapped plumbing threads and did not go down far enough on the tap the first time. I first put the tank on a couple of old pillows to protect the paint and just used an adjustable wrench to drive the tap. This means I caught a couple of threads on the petcock and got tank metal in the threads. I got to tap the tank deeper and go back to the hardware store to buy a die to clean the petcock threads.

If you have a friend with plumbing experience and the tools you could save money and time here. It might actually be cheaper than the way I did it to just take the tank to your local plumber. My wife says I just used it as an excuse to buy the tools.

I installed the petcock with liquid Teflon and let it dry overnight before assembly. The result is a cheap nice looking high flow petcock that should last years and be very easy to replace when it fails.