I have new sealing washers for the petcock screws and I see that one side is fiber and the other side is metallic. So which side does the fiber go against? The petcock base or the screw head?
 

I’m going to guess that the fiber side goes against the petcock base and the metallic side goes against the screw head. Otherwise the rotating screw head might tear up the fiber. Hope it seals!,

Your guess is how I install them. 

Trying to remember though...  not sure I ever had fiber ones.  I thought they had a rubber seal.

The original ones are always hard as a rock, so I ordered a batch of them from Yamaha awhile back. This isn’t the first time I’ve used them, but it is the first time I noticed there was a difference from one side to the other. It’s installed and the tanks full with no leaks yet. Long ago I bought four of those petcocks that are for the big quads but they bolt up nicely to the enduro tanks. Just used the last one on this CT1C, so I ordered two more for inventory! Just need a new back tire and I am done with his bike. Can’t wait to put some time on it.
 
 

They are metal in the middle surrounded by fiber. They go on either way. I’ve used them on most of my bikes with no leaks. Newer style is metal in the middle surrounded by rubber. Either way on them too. Five or six installs with no leaks. Install them however they come out of your hand. 

Things i didn't know--about yamaha fiber washers.
Man the pipe looks nice on your CT1. Shed looks nice compared to my mess.

I recently replaced the original petcock on my CT1 and those fiber washers were between the screw head and the bottom of the petcock. There's an oblong o-ring that seals between the tank and the petcock. I used a generic ATV Yamaha style petcock that bolts on just right, and it came with new fiber washers. I put them on the same way as the original was. However I've been using regular gas from the gas station, and I just found out that when it's turned off the petcock still leaks a little bit of gas out into the carburetor. I just put a little bit of wheel bearing grease on the face of that four hole gasket inside the petcock, and that seems to have sealed it for now. I know it was turning off when I first got it because I removed the tank with it turned off and it wasn't leaking, but when I removed the tank today was still dripping when it was turned off.

That ethanol is probably drying out the rubber already. The neighbor across the street with vintage motorcycles actually buys high octane no ethanol fuel at Home Depot, designed for weed eaters. It's about seven bucks a gallon, and he said it actually will clean out your carburetor. Also if the weed eater or whatever is stored for a long time, it'll start right up. Alcohol is for drinking, not to put in your gas tank!

If you end up having to replace yours because of leaks, this is the one I’ve been using. It is a Yamaha part and I have them on four of my bikes with no issues. I got them cheaper a few years ago……  
 

There is a thread on here detailing the different part numbers for original Yamaha petcocks that will work, they can be had with a  3-6-9 o’clock outlet, I normally use Yamaha part # 2HR-24500-02-00 on a 75-76 DT400, it has the 6 o’clock outlet. They look a little different than original but work great as they are genuine Yamaha parts, and are usually cheaper than buying all the bits and pieces to rebuild one, the ones I use to rebuild I had a 75% success rate. I personally would rather spend a little extra for the Yamaha part number vs. the $10.00 generic ones and not worry if they are actually shutting the fuel off completely. Another note on the replacement petcock I can’t remember but one of the brass tubes was longer than the original petcock, I cut it down to the same height as the original using a pipe cutter so the reserve fuel function would be the same.