Only about a month ago and within 20 miles of driving after installing a brand new Dansk "banana" muffler, I noticed something that seems very unusual on my 1974 2.0 Bumblebee. The motor has it's original fuel injection.

The car is currently on jackstands at a body shop for repair of bad repairs and with the muffler exposed, I noticed discoloration of the paint. Looking at the four pipes where they bolt to the heat exchanger both driver (left side) pipes and the left passenger side pipe are now discolored to a light tannish-white color while the far right passenger side pipe is still the original gray. The color is like that of a spark plug running lean.

Could this be a sign that the motor or at least 3 of 4 cylinders are running lean? I know it sounds goofy! The motor starts easily and seems to run fine.

Has anyone experienced this? Any other theories?

get the motor hot and measure the temp of each exhaust oort at the head if possible. see if you have any cylinders running hotter than others. also neasure at the muffler inlets.

The muffler inlets are what is so discolored along with a band all around the entire banana on the left driver side where both muffler inlets are discolored. I have SS heat exchangers; nothing to see there.

Thanks for the advice. It seems apparent that three cylinders are running much hotter. Does anyone have experience or a theory as to why certain cylinders would run much hotter than others?

Its a bit of a guess w/o empirical data. Try to measure temps near each exhaust port if you can (infrared thermometer from Harbor Freight works good for this). If there is a big variance I'd look deeper. If there isn't I'd chalk it up to something about the flow or resonance in the exhaust system and nothing to worry about.

How long has it been since the injectors were cleaned? You could have one that's not closing all the way and causing that cylinder to run rich. If you pull the spark plugs and read them, are there any clues there?

I'd get the muffler ceramic coated while its still new