Ok everything was running good on my 69 Malibu until this morning. It backfired so I let it sit until lunch and it backfired again. So I let it sit and this afternoon it started. I drove around and when I put it in park and shut it off I heard a loud thump. I am scared to find out whats wrong and how much its going to cost. Anybody have problems like these?

Back fireing out exhaust or carb.?

I would check timing.Or time for carb. rebuild.

I would definately check timing to see if your distributor might not have been held down securely or something.

Less likely- maybe your timing chain jumped a tooth.

-Bob Cunningham

It backfired out of the carb and burned my air cleaner.The carb is a new one with an electric choke. It started for me today but when I turned it off it made a sudden thud and shook the car.It sounded really bad.
thanks for the help

New carb,have you checked floats and air mix ?

Timeing will make it back fire out of carb.

Initial backfire could have been caused by timing chain stretch,noise you heard could be that the chain actually jumped on the gear.I would bring #1 to TDC pull cap and see where your rotor buttons at.