So I decided to replace my cam, and I noticed that my brand new chain had indeed jumped three(!) teeth on my brand new gears. This is what's been causing the backfire that's been causing my ring gear teeth to get cut off by my starter gear. Why did the chain jump? It may have had something to do with the aftermarket woodruff key that I bought. I noticed when I was removing the old cam, that the crank sprocket seemed loose on the crank/woodruff key. I checked the sprocket on an old crank that I had lying around, and it fit really snug. I don't know how I missed this when I was putting my engine together, but I guess I did. I'm not trying to blame the company that sold the woodruff key (you can guess who they are) since I should have made sure that everything was snug before I buttoned up the engine. Needless to say, however, that I'll be replacing the aftermarket key with a stock on now...
I'm just glad I finally figured out what the problem was...3 months later...