I have a 79 Ford F100 with a 300 Straight six and it will not Idle or even stay reunning when I let off. It seemed to be running rich so I installed a new carb. After installing a new carb it ran fine for about 5 miles then it started acting up again. It runs great when I have my foot on the gas. I think it may be the catalytic converter. I know it is in tough shape, but could this be causing the problem? I would really appreciate any help.