I'm getting some backfiring out my tailpipes when I let off the gas. I have a 65 with a 194, 3spd manual and split manifold. It started doing this shortly after I replaced the carb(1bbl Rochester). I've also got a surging problem at cruise(about35-40 mph), Is this because of the carb? It is a rebuilt unit from Kanter in NJ. The choke on my other one quit working, so I changed it out. Any help is appreciated.