Definately check the cat.Did you change the carb because you thought it had a problem or just wanted something different? Why I ask is because my dad had a van he thought was low on power and it started smelling like a rotten egg well needless to say he nearly caught the thing on fire one day we were pulling a boat and it started lugging real bad so we pulled over and the pipe from the manifolds to the cat were nearly incandescent. I would defintely look into it.