1996 Skoda Felicia confusing problem, maybe carburator

Other Category problem
1996 Skoda Felicia 4 cyl Front Wheel Drive Manual

I have been having a frustrating problem with my car. Even my local mechanic hasn’t uncovered it as of yet. My car is a 1996 Scoda felicia, I live in the Dominican Republic so maybe that car isn’t available there in the US. It has a carburator, ( just to give some information about its type). Well every morning the car starts easily but when I want to move it bogs out. Up until lately every time I entered a long underground tunnel the car would shut off on its own, so I have been avoiding tunnels. But now the car does the same thing in other places also. I took the cap off the carburator and noticed the air filter was very dirty (it’s rather new). This made me think there is oil getting in somewhere but I really don’t know. The car also has problems when there is dew in the morning until its dry. What can I try? I hope you understand my problem, its very difficult to explain well.