rough idle

ok i just got a 90 pickup with a 22r that has 135k on it. it sat for the past two years so i went ahead and done a full tune up and had to get a new muffler and it ran great. well its been about a week now and it started to idle rough and when im driving if i let off the gas it backfires a little. well i noticed last night that the pipe coming into the cat was red hot. when i drove it today the backfiring got way worse when it backfired it blew a big hole in the muffler. can anyone direct me toward what to check.

Sounds like a clogged cat. Those things have screens in them that can get clogged up pretty easy after time or if the motor is being abused. Its backfiring because the build up of exaust pressure, which can make it through the clogged screens. Most places want alot of $$$ for cats. So I recomend a free flow cat or buy an exuast system from the junkyard. That way you get a cat and muffler. They cant sell you just the cat. Make sure its not too old though.

It's the carb. Had the same problem: backfires, erratic idle, hot cat, HOLES BEING BLOWN IN MUFFLERS! I looked into rebuilding the stock carb, costed too much, spent more and went with a Weber 36DGEV. Took about 20min. to install, eliminated some of the emmisions equipment, runs great, performs alot better!

Yeah, or that. Lol.