Help Please Farish Hopper Coupling Problems

[georgehgv]

Hi. Finally time to run some freight on new layout, got 2 Farish Bogie Hopper Freightliners, 2 Farish IIA Bogie Hoppers, 2 Farish Axis Bogey Intermodels.

Problem I am having is the couplings don't want to stay coupled, the Axis has an NEM on one end and a hook on the other and a loop on the other Axis, how do I fit NEM to both ends please? Anyway even on the NEM couplings they do not want to stay coupled and reluctant to follow tack derailing, is it that the wagons need some weight ballasting they seem very light?

Carriages I have all seem to run ok and don't keep detaching.

Thanks.