Th Petcock on all Honda bikes from the 1970's to the early 1980's fitted to the CBX & DOHC bikes have a tendency to give way just when you don't want it. The Super Sport Shed Supplies a genuine Honda replacement gasket and the required screws to upgrade before or even after disaster strikes, trust me I have personally been there more times than I want to remember. Do this if you are rebuilding any bike or have a bike that has to be upgraded, trust me any age, mileage or condition makes no difference it will fail.
The good news is the fix is relatively simple and cheap which is available here https://thesupersportshed.com/product/petcock-repair-kit/, the main thing is that you have access to a 3mm tap a pillar drill, to ensure the drill enters the petcock at right angles is perpendicular.
If you do not have this facility or tools we can upgrade for you for a third of the price of a new one here https://thesupersportshed.com/product/petcock-overhaul-service/ I have done this upgrade many times and have found the perfect way to do it, having refined the process over the years, taking this approach limits the amount of swarf that can enter the petcock on disassembly. First things first are to secure the petcock in a hand vice making sure it is as mentioned at right angles and perpendicular to the drill bit. Use a 2.5mm tapping size drill in preparation for the petcock to be tapped, using a 3mm second tap (taper is not required as it's a soft zinc alloy).
OK now both sides have been drilled put your tap in the drill chuck and start the thread by pulling the drill press handle down to (not too hard but enough to start the thread) the petcock and twisting the chuck to start the thread, this ensures the thread is straight into the drilled hole. Twist 4 or 5 turns, then twist it back to remove the tap.
The next step is to carefully remove the rivetted material to allow the removal of the faceplate and "innards" of the petcock. Use a 5mm drill to carefully drill the zinc alloy just below the surface of the faceplate, avoid removing material from the faceplate itself (see picture). Once you have done this remove the petcock from the hand vice and tap the 3mm holes (before you split the tap itself) to the bottom taking care not to break the tap off!
Now for the part where you need to contain the petcock in a tray to avoid the locating ball bearing going walkabout, along with the spring behind the ball bearing and the pressure spring (see pictures below before proceeding). Carefully lever the faceplate off with a small screwdriver, start in the middle and lever your way out on both sides, it will give way.
After the faceplate comes free be very careful of losing the locating ( in the side of the tap component) ball bearing and springs as previously mentioned. Remove the old gasket/packer and replace it with the new one (see the wear on the old gasket, this was dripping onto the carbs and engine).
Now for the fiddly fit, carefully fit the parts back together how they came out, firstly aligning the base plate (the plate that pushes against the gasket/packer) indent at the 4 O'clock position in line with the locating slot for the ball bearing. Insert the pressure spring and carefully push the faceplate and tap into the slot as per the picture below, hold together with a finger and thumb and with difficulty get the two screws into the newly drilled and tapped holes. Carefully tighten the two screws ensuring they locate over the two existing pillars without catching.
Now it's all done ready for re-fitting. If you feel you cannot undertake this task yourself we will be more than happy to do this for you, the service can be found here https://thesupersportshed.com/product/petcock-overhaul-service/