Severe BACKFIRE
 

I wonder if someone can help me here!
I have a 84-5 letters- this one have fuel ingection with a severe back fire after the car is warm.
The problem come when I take off the gas pedal or decelerate to change gear 1 to 2, 2 to 3
and 3 to 4 mostly. this problem blow out my cat. I replace the cat and the it blow my new seals.
If I replace the seals again I am sure something else can blow down there. I have no idea how
the this can be solve. I took it to mazda dealer and they couldn't figure out the problem ( they
do not have any oldschool guys there any more). Please any Idea. Thank you!

Did they check the timing? How about the ACV? (air pump)?

cheak the fuel mixture it sound like if its way too rich

I do not think they check the timing at all or anything. I have a way to get a timing gun, but how I do it my self and also how would I know or check the fuel mixture? What is the ACV?