Popping in my air box

[352mustang1987gtcon]

I have a 1987 gt convertible and I’m try to get it to run right have replaced the coil, sparkplugs ,wires,cap roter ,pip and try different tfi module but still a back fire/ popping still comes throw my air box need help motor is all stock

 

[General karthief]

It may be an indication of a stuck valve, I'd do a compression test.

 

[352mustang1987gtcon]

Ok I will check but also this problem comes and goes as I drive it

 

[Deleted member 215073]

Are your catalytic converters clogged?