Birchwood Casey has a nice cold bluing solution. They also have a brown/bluing solution that usually comes out sort of a plum color. Experiment with it and with different bluing solutions. Cold bluing can be removed fairly easy. The most important part of bluing is to make sure ALL oil is removed from the part you are going to blue. The oil from your skin can even impact it. The one with a rust spot could go a couple of ways. If it's a collectable I might leave it alone and just do what you are doing. If not collectable, I'd try using a little 0000 steel wool with gun oil making sure not to harm the bluing around it. You could wrap the steel wool around a small pencil eraser to lightly rub the spot. Sometimes it's best to leave it alone. The cold bluing typically doesn't match the factory finish so the touch up would stand out.

If this is an aftermarket carb, sometimes the throttle cable is not adjusted proper for the fit. Make sure the throttle plate is closing all the way and the choke plunger is working properly. Try some starting fluid and see if it makes some noise if it does it will run just have to get the mixture right.

Make sure you have spark at the plug, you may have a good spark plug but it may not be firing when you plug it in.