I would suggest that the zeniths be rebuild .
i have these on my 230/110 , 220S.111, 280S /108. All are dependable and work perfectly if the fuel delivered is clean and setup correctly . Ages ago i got a German made carb synchronizer for the Zeniths JCwhitney still offer it,Excellent product.

The carb service section in the 108 Service manual carries a detail diagram for the fuel flow in the carb jets . With this understanding of the Zeniths you will not have any problem with them.
good luck
mak