New Cat gets beet red and car runs rough

[inspector_mike]

Hi all. hope someone can help me out there. I have installed new 2 1/2 inch exhaust from manifolds to end. installed 2 old cats, 2 new magna flow mufflers and x pipe configuration. passenger cat got beet red, car started to bog down. replaced new cats with 2 new magna flow high flow cats and magna flow mufflers. same thing happened
mechanic said that the old large pie shape CAT was a 3 or multi flow cat and the new cats are one way flow that do not work with the unburnt gas from the carb and that is the reason why the cat is getting red.
can someone help me
not sure why only one cat gets red only>

thanks Mike

[Wallington]

1980 301?

[FormTA]

Could it be running rich and loading up cats with raw fuel.

[inspector_mike]

Thank you for the responses. adjusting the carb fuel for richness, replacing the plugs worked
Thanks again
Mike from Canada