I had another thread, but i feel the problem has moved more to exhaust so help me out.

My 91 305TBI overheated on the way home one night, water pump failure. So i put a new one in and it seems to be...rocking. So i tore it down, replaced spark plugs, check compression did everything and its all okay. So now i'm thinking its the gasket that connections the stock headers to the stock Y pipe. Would this failed gasket cause the car to rock, but when in gear, backfire?

 

no the gasket would not cause that, but if its bad replace it.

did you unplug anything, by accident maybe, when you changed the pump? sounds like something timing or fuel related is wrong.

not sure what you mean by "rocking?"

 

Turns out it wasn't that, i finally found my 3 week old problem.

There is this...vacuum port on the intake manifold in between the dizzy and secondary vacuum. I accidently broke the plastic piece connecting that and when i held them together it ran 100x better. Now i just gotta go get plastic cement tomorrow.