Duel air pump not working for one side?

[KFav93]

I have an air pump with 2 hoses. One hose runs to one of my 20 gallon tanks and the other to my other 20 gallon tank. The one is working fine. The other one does not have a consistent flow of bubbles. It just keeps skipping and spitting out bubbles. It was working fine before I left for the weekend on Friday. I just want it to go back to having a consistent flow of bubbles. Any suggestions? Could it be the air stone?

[Fresh2o]

It could possibly be a clogged air stone.
Have you tried taking the pump apart? I have not worked on one in a long time, but I remember having to change the flapper valves and rubber diaphragm when there was obvious wear and poor performance.