What causes my 1965 4 speed mustang to backfire and sometimes stall?

make, model, year? backfires are spontaneous burning (exploding) of unburnt fuel outside of the combustion chamber. suspect bad spark plug/s, ignition coils, ignition timing, computer, leaking fuel injector, etc. scan for trouble codes, then post back. because the problem is intermittent, problem manifests only when hot (engine at operating temperature) do tests for both cold & hot conditions. test resistances (ohm) of suspected sensors: cam & crankshaft position sensors, ignition coils (if possible),(search the web for the recommended procedures). also test voltages at the computer (search the web for the pin outs of the computer of your car). also check associated relays (like for the fuel pump, etc.) a bad relay may have its coil open when heated, then becomes good again when cold. i suspect the car may have a good fuel delivery but the sparks are not coming in on demand, thus backfiring.

It might need a tune up.

I have a feeling your fuel pump is on its way out...but start by changing your fuel filter first, should be under $20....ie..not enough fuel getting through..

Suggest you check the spark plugs for carbon buildup. this will cause a backfire.

Engine system needs inspection on case of backfire:-----

Check out related help links to troubleshoot the vehicle backfire issues:-----

Feels like backfire from engine when decelerating?

http://schematicsdiagram.blogspot.in/2012/02/feels-like-backfire-from-engine-when.html

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Jeep Backfires?

http://technoanswers.blogspot.in/2012/02/jeep-backfires.html

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Nissan Pathfinder stalls and bucks on Acceleration?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-stalls-and-bucks-on.html

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Nissan Pathfinder Backfires?

http://technoanswers.blogspot.in/2012/02/nissan-pathfinder-backfires.html
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These will help.
Thanks.

Fuel filter.or catalitic converter. I had 44000 on my Monte Carlo when it acted like it could not breath. The catalitic converter was clogged. I got a new high flow type.GM covered my replacement.

I would suspect a burnt valve. An engine compression test will verify this.

replace the accalerator pump in the carbrator this is located at the bottom of carb. or front above fuel filter! this should cure the hiccups and problem.

Buy a new car!