AOA ALL
One of my friend is a CNG mechanic and he has done multiple times putting engine oil directly into carburator.
Once I asked him why he did this he told me that due to constant running on CNG car piston and carburator gets dry so they can get rust causing problem with the engine so this oil will put a layer on them to make it rust free.
I asked my uncle who is an engineer at a OGDCL Rig and he told me that this oil worked as grease for piston as they are not an easy reachable this trick is good for them. After pouring oil the layer gets on piston and extra oil is been washed with the petrol.
Of course it causes a harm to plugs but then I remembered that when ever my friend done this he asked me to change plugs as soon as possible even he opens old plugs and wash them with petrol o remove that dirt.