On a previous episode of how I screw things up and then fix them, I drilled out the carburetor of my 1983 Honda XL600R to remove a stubborn air screw that had the head stripped off. In doing this, I broke off some of the threads. I determined that the threads were 0.75mm pitch, and the air screw was 5.74mm in diameter. I assumed that this was really a M6X0.75mm thread, so bought some like bolts from McMaster. Today, I threaded one, and it actually fit! It was a little tight, but it did thread in all the way. The threads probably need to be chased. Fortunately, I should be able to grind one of the new bolts into a plug tap, because the carb is just aluminum.

#Thread Repair

The first thing I did was clean the outside area near the broken threads with Carb cleaner. I figured it was a decent enough solvent that wouldn't leave much, if any, of a residue.

Next, I covered a bolt in thin layers of wax and soot from a candle. Basically I wanted a surface that wouldn't stick to the JB weld, or would be weak enough that the bolt would release. I also wanted this coating to be thin enough that the epoxy would form into the threads. For this, I got the bolt sooty, dipped it in hot wax, then lightly paper toweled it off, checking that the threads still existed.

Melting Beeswax to prevent epoxy from sticking to the bolt.
Sooty bolt
Bolt getting extra sootified
Bolt as I glued it in, hopefully it won't stick!

With my waxy, sooty bolt, I had a form on which to make threads. I threaded this bolt into the carburetor, but not all the way. I suspected I would need to screw it in to break the epoxy's hold. I then applied my favorite 2-part epoxy to the area, making sure to push the epoxy into the threads decently. I'm hoping it will release, if not, liberal application of heat should help me, just need to remember to drain and dry the gasoline from the bowl...