exhaust backfire

[86runner]

i have a 86 4runner. i had hollowed out the cat because of it being broken up inside of it. i now have a backfire when under load(like at 4 - 4.5 r.p.m's) could that be it?
also, is it common where the y-pipe conects to the exhaust manifold to keep loosing up? it also won't seal right even with a new gasket?

[86taco]

I have a 86' 22re and hollowed out the cat and it didnt hurt anything. Check your ignition timing just to make sure thats not the problem. On the y pipe Are your flanges straight ? Is the rest of your exhaust system tightly secured. If it is able to bounce around excessively this will cause it to loosen up and leak. I welded in a piece of 3/8 rod to my pipe and welded one onto the frame and then cut a piece of rubber, cut some holes in it and whalla a cheap exhaust hanger.