Rough running, backfiring, and smoking white/bluish exhaust scream plugged muffler to me. Have you ever BBQd it? I had the same issue, and it cleared up with a good muffler BBQ.
Even at 100 psi the cart should be running OK I think. Not optimal, but not horrible either.
Check out this thread:
http://www.buggiesgonewild.com/gas-y...-hot-pics.html