If you only drive the car on short trips (less than 10 miles) without heavy acceleration or extended runs at higher speeds I expect that there could be a build up of soot/carbon in the exhaust system.
I have used the “water” trick to clean surface carbon and soot out of an engine. It is a trick I learned from my father.
Drive the car quite a bit to get everything up to a normal operation temperature.
Remove the air cleaner and start the car. Slowly pour a small stream of water into the carburetor. You will need to keep opening the throttle so the engine keeps running. It will stumble some and miss but keep it running. Back off on pouring the water and let the engine come up to speed. You do not want to stall the engine. Then keep doing this for about a quart of water. You should see steam coming out the tailpipe.
Some people have done a similar treatment with products like Seafoam, Marvel Mystery Oil, and Gumout.
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