Need help figuring out why my 78 2.0 Spider is running with extremely hot exhaust, popping and lacks power. After running the car really hard last fall, the exhaust pipe cracked off just behind the header. Another Alfa club member advised I might have an issue with plug fouling but should be able to limp home (about 10 miles). Making lots of noise, I got most of the way before the car started to get fluffy when reving and lost virtually all power. Got the pipe re-welded and decided to add a cat to make the car legal and more environmentally sound. Tried re-tuning the Webers and timing, but couldn't get it to rev without popping and serious lack of power. After re-inspection by the muffler shop, the cat core was completely melted and in a wad in front of the muffler. I don't know where to start searching for the problem. Electrical/ignition maybe? Burnt exhaust valve maybe?