why isn't my main part not moving but the rest are?

I made a weld and position script with the help of this site. The primarypart of the model wont position itself but the other parts position their self. I get no error on the output, I honestly don't know what is wrong.

I set the primary part in the model as main. heres my script

local Lighting = game.Lighting
local Vest = Lighting:WaitForChild("Flak Jacket")


game.Players.PlayerAdded:Connect(function(player)
    player.CharacterAdded:connect(function(character)
        character:WaitForChild("UpperTorso")

        local ClonedVest = Vest:Clone()
        ClonedVest.Parent = character

        ClonedVest:SetPrimaryPartCFrame(character:WaitForChild("UpperTorso").CFrame)

        local Weld = Instance.new("Weld")
        Weld.Part0 = ClonedVest.Main
        Weld.Part1 = character:WaitForChild("UpperTorso")
        Weld.Parent = character:WaitForChild("UpperTorso")
        ClonedVest:SetPrimaryPartCFrame(ClonedVest:GetPrimaryPartCFrame() * CFrame.new(0,0,2))
    end)
end)

do i use inverse? and how?