Just got my car back on the road after a long frame off restoration. I noticed that at about 3500 rpm on acceleration I am getting a backfire/popping in the exhaust and miss. The car had the same problem before the engine and carb were rebuilt. I noticed when I was working on the Carb many months ago that there was quite a bit if play in the throttle valve shafts. I had the carb professionally rebuilt and the car runs really well when just putting along. I did verify that there is a vacuum leak at these points. I am running a stock 396/325 horse except for an Edelbrock performer cam, headers and Petronix ignitor points replacement. Are the loose throttle shafts causing the problem. If so what should I do to correct. I would prefer to keep this carb since it is the original. Thanks.