My gun propells my players forward uncontrollably?

Hello!

So recently, I've been trying to make an FPS. Everything's going well, but I have one issue: My players get propelled at speeds (ranging from walking speed to flying through the sky) uncontrollably (until I come out of First Person).

I've made the arms un-collidable (if that's a word) as well as the gun. I'm using CFrames to move the arms, gun, etc.

I would add a video but my computer is being odd. Sorry.

Thanks for considering, MaximussDev.

EDIT: Main script.

repeat wait(1) until game.Players.LocalPlayer.Character:FindFirstChildOfClass("Tool") and game.Workspace.CurrentCamera.CameraType ~= Enum.CameraType.Scriptable

local camera = game.Workspace.CurrentCamera
local viewModel = game.ReplicatedStorage.viewModel:Clone()
viewModel.Parent = camera
local weapon = game.ReplicatedStorage.Weapons[game.Players.LocalPlayer.Character:FindFirstChildOfClass("Tool").Name]:Clone()
weapon.Parent = viewModel

for _, piece in pairs(game.Players.LocalPlayer.Character:FindFirstChildOfClass("Tool"):GetChildren()) do
    if piece:IsA("Part") or piece:IsA("UnionOperation") then
        piece.Transparency = 1
    end
end

local joint = Instance.new("Motor6D");
joint.C0 = CFrame.new(1, -1.5, -2); -- what I found fit best
joint.Part0 = viewModel.Head;
joint.Part1 = weapon.Handle;
joint.Parent = viewModel.Head;

local function updateArm(key)
    local shoulder = viewModel[key .. "UpperArm"][key .. "Shoulder"]
    local cf = weapon[key].CFrame * CFrame.Angles(math.pi/2, 0, 0) * CFrame.new(0, 1.5, 0)
    shoulder.C1 = cf:inverse() * shoulder.Part0.CFrame * shoulder.C0
end

local function onUpdate(dt)
    viewModel.Head.CFrame = camera.CFrame
    updateArm("Right")
    updateArm("Left")
end

local aimCount = 0;
local offset = weapon.Handle.CFrame:inverse() * weapon.Aim.CFrame;

local function aimDownSights(aiming)
    local start = joint.C1;
    local goal = aiming and joint.C0 * offset or CFrame.new();

    aimCount = aimCount + 1;
    local current = aimCount;
    for t = 0, 101, 10 do
        if (current ~= aimCount) then break; end
        game:GetService("RunService").RenderStepped:Wait();
        joint.C1 = start:Lerp(goal, t/100);
    end
end

local function onInputBegan(input, process)
    if (process) then return; end
    if (input.UserInputType == Enum.UserInputType.MouseButton2) then
        aimDownSights(true);
    end
end

local function onInputEnded(input, process)
    if (process) then return; end
    if (input.UserInputType == Enum.UserInputType.MouseButton2) then
        aimDownSights(false);
    end
end

game:GetService("UserInputService").InputBegan:Connect(onInputBegan);
game:GetService("UserInputService").InputEnded:Connect(onInputEnded);

game:GetService("RunService").RenderStepped:Connect(onUpdate)

Used from a tutorial by @EgoMoose.