BarelyAwake: Yes the sponge is a proper air filter sponge, no I didn't oil it, but I think I may have squished it a little in getting it in there, I'm pretty sure I did. I didn't think about that being a problem; I thought if there were a restriction problem I would just feel it, but I was wrong. I'll try another piece and make sure it's not squished at all, and if that don't work maybe I'll do that B&S you suggest. The PVC is connected only to the carb, nothing else holding it, although I think the plastic box at the end rests on something back there a little bit. But it's all metal where the carb is, I wouldn't think it would be a problem, do you? After all, the whole thing(the part I added) doesn't weigh much, I'm pretty sure it's under a pound, and at most it can't be much more than a pound. As far as rain, I don't ride in the rain or leave it outside in the rain, so that shouldn't be a problem, although I would like it to be water resistant just for the sake of it. Mine may indeed be quieter, if the PVC is better at doing that than the tubing, but also because the tubing I used was thicker than shop vac hose; it's some kind of pool drain tubing I think.
As far as the adjustment on the fuel/air mixture, the engine was running great before I did this modification, so I have to ask why you say that? I don't know how to adjust the fuel/air mixture, or what would cause it to be necessary, so is it possible that even though it was OK before, it needs to be adjusted now anyway due to the modification?