Weight Paint issue with Makehuman rig

i have been having problems with my makehuman rig. When i move the arm, the mesh decides to move in a very jagged and ugly manner, whereas before the mesh would deform more smoothly.

i used the vertex groups to quickly assign vertices to bones (so i could quickly rig the vest i made for the character)

but this made all the vertices be influenced by the bone by 100%. not with the default values that the imported mesh started off with.

please help