I don't know if you found this already or not, but this is a breakdown of all the parts on the Carter SPX 2936.
http://kartingdistributors.com/pdfs/.../2936-4015.pdf
Your new belt looks correct to me in the pictures. Make sure you have the belt installed in the correct direction. I'm pretty sure you know this, but the TC 30 belt is angled on one side, and should not be put on backwards.
We own a few Carter SPX karts. We didn't run them this year, but I can look at our karts this weekend for a comparison to your pictures if you'd like.
If it is too frustrating to figure out your problem, you could have a bad or worn torque converter set up. Perhaps a previous owner messed with the springs. New, complete TAV 30 / TC30 units run about $100 on ePay. Your chain should be #40. They're not Comet units, but they should be just fine. I'm not sure if Comet is still around.
Luke