Almost every Tillotson carb that I have (reluctantly) rebuilt for customers and friends needed the lowest horizontal passageway to the GAV well drilled out. It's the lowest passageway in the carb and gunk tends to settle here. Poor performance and even bucking under acceleration result when this passageway is clogged.
You can see the plug to this passageway in your photo at the lowest point of the carb's lower body. Carefully drill that out. But first, remove the GAV hardware so that you can see down inside. Start with a smaller bit than the size of the plug. Once a hole of sufficient size has been drilled, you may be able to pick the plug remains out, or it may come out with the bit. This goes directly into the bottom of the GAV passageway. The passageway is not as big as the plug; it's quite small where it exits into the GAV well. Take a stiff wire and shove it through the hole you just drilled out as far as it will go. It should poke into the GAV well at the bottom. Look down into the GAV and verify whether the wire goes through all the way. If you don't see it poke through, the passageway is blocked. The crud is almost always compacted tightly and doesn't easily pick out. Use a small bit to carefully drill out the crud. It should come out easily with the drill bit. The drill bit should exit into the GAV well. Then go to the next larger bit and drill out more crud. Keep going larger until the bit feels as though it's starting to drill into the pot metal body and not crud, which definitely feels softer and spongier. Stop there! The hole is big enough. If you drill the hole too big, it will throw off the GAV adjustment. I can't recall the correct size of the bit, but it is relatively small.
Now plug the hole you drilled with lead solder pounded into place or tap the hole and screw in a small bolt, coating the threads with an epoxy to prevent seepage. Don't go in too far or you'll block off the passageway hole near the plug. Once the bolt is in place and cured, hacksaw off the part of the bolt still sticking out. File smooth. Replace the GAV hardware and allow the plug's thread epoxy to cure before starting the car.
You should notice an improvement in performance with this hole drilled out. All the new gasket kits and blowing through the passageways with compressed air will not clear this stubborn passageway. Soaking in solvent won't do it, either. It must be drilled out to clear the way.
Please let us know if this passageway is clogged in your carb. I'd be surprised if it isn't.
Marshall
