I have a good way to silence the rear bolt of your pro-carb. When my roommate came up with this one I thought he was nuts.... Until I tried it.
All you will need is a small piece of 3mm neoprene; we used wetsuit material, some silicone (rtv) and denatured alcohol or another similar solvent to degrees.
1. First step is to remove your valve and then cut a piece of the neoprene that will cover the valve face. Poke a small hole in the center of the pad for the valve pin to pass through. I used a leather punch for this. While you are cutting, cut an extra pad from you're material.
2. Clean the valve face with whatever solvent you have handy, even rubbing alcohol will do here, you just need to remove any oil from the surface. Take you're pad and the silicone, put a small amount of adhesive on the pad and slide it over the pin. Make sure it is firmly pressed to the face. I used a cardboard disk with a hole poked in the center and two rubber bands for clamping. Let that sit overnight.
Now re-assemble the valve and swap the extra pad you cut for the stock cushion. That's it. You will like the results, I am sure.
