I have a 1988 Toyota Truck 4 Cyclinder standard pickup with 2 Bbl Carburetor.

The original engine has 155,000 miles and still has alot of power and take off where I still get the same gas mileage as it got when it was new. It always passes the Virginia State exhaust emissions test.
The issue is the exhaust has carbon or some sort of odor that is especially strong when in a Parking garage or when the engine is running in my two car garage. This odor has been around for the past 4 years and I have put in new plugs and tune up and nothing seems to get rid of it. I have never tried any gas treatment or cleaners.

Please advise if I should put a specific type of cleaner in my gas to get rid of the carbon odor or what is recommended to get rid of this exhaust smell?

 

The odor from the exhaust is clearly going to be stronger in an enclosed space. If you are passing emissions inspections, you are fine. If there was a fault with the O2 sensors or Cat, the inspection will pick this up.