I inherited a 1979 2.3L Mustang, it has a 2BBL Holley 5200 carb I think. It hadnt run in a couple years... it looks like a lot of failure parts were replaced somewhat recently. So far since I have got it, I replaced the mechanical fuel pump, fuel filter a couple times, new gas, new battery, and new plugs. I took apart the carb and all parts seem to be up to date and rebuilt some years ago. I can start it ok but after about 20 seconds, the idle starts to drop, the engine bucks hard and eventually shuts off. A little white mist comes out the carb and some white misty smoke comes out from under the exhaust manifold. I checked the electric choke and it is getting about 6.23V, so Im not sure whats wrong. Any ideas?
could be that the float level is set too high (or stuck float) and is flooding the intake manifold with fuel causing it to run fine for a few minutes and then flood out - giving the bucking you describe.
I had this problem with my '85 2.3. Make sure the screws between the throttle plate and air horn are tight. They are famous for vibrating loose.
Take off your air cleaner and grab the carb with your hand tightly then try to move it. If the carb has play, 90% of the time its the base plate being loose from the air horn. Major vacuum leak!!! I used LOCTITE thread-locker on the screws and the problem never came back.
While the carb is off and you are tightening the throttle plate screws (torx), make sure all the screws all over the carb are good and tight. These carbs are known for vibrating loose.
Also if you are having problems restarting the engine after a long drive, in the summer, you need a phenolic spacer between the carb and manifold to displace heat and some high-temp insulation on your fuel line from the fuel pump to the carb.