how to fix motor spinning weridly?

this script is making the motor cycle spin weridly?

wait(0.1)
Players = game:GetService("Players")

seat = script.Parent-- the driving seat
car = seat.Parent

Player = nil

forwardsSpeed = 80--if you removed the Configuration folder, it defaults to this speed forwards
reverseSpeed = 10--if you removed the Configuration folder, it defaults to this speed backwards
StartTime = 1--how long (in seconds) the car should wait before starting up. This is dependant on the starting sfx

engineBlock = car:FindFirstChild("EngineBlock")--maybe someone doesn't like sound?

lightsOn = false-- whether or not the lights turn on
carRunning = false--whether or not the car is running

RemoteControlled = car:FindFirstChild("ControlByRemote")--this is so the car turns properly

function CalculatePitch()--this returns the pitch that the engine should be at when its travelling
    return 1+engineBlock.Velocity.magnitude/100
end

Configuration = car:FindFirstChild("Configuration")-- so you can change the stats of the car
if Configuration then-- if we found an object named Configuration in the car then do this stuff:
    local ReverseSpeedValue = Configuration:FindFirstChild("Reverse Speed")-- do we have a reverse speed?
    if ReverseSpeedValue ~= nil then
        if type(ReverseSpeedValue.Value) == "number" then
            reverseSpeed = ReverseSpeedValue.Value
        end
        ReverseSpeedValue.Changed:connect(function()-- level 1 scripting: go
            if ReverseSpeedValue.Parent ~= nil then-- this script works, but there are some things
                if type(ReverseSpeedValue.Value) == "number" then-- to make it look a little better
                    reverseSpeed = ReverseSpeedValue.Value
                    UpdateVehicle()
                end
            end
        end)
    end
    local ForwardsSpeedValue = Configuration:FindFirstChild("Forwards Speed")

        end
    end
end

function SurfaceGuiBrightness(part,on,bright)-- this is so the brake lights dim when we drive
    for _,i in pairs (part:GetChildren()) do
        if i:IsA("SurfaceGui") then
            i.Enabled = on
            if i:FindFirstChild("Frame") and i.Frame:IsA("Frame") then
                i.Frame.Transparency = bright and 0 or 0.5-- scripting level 4: go
            end-- for simple statements, you can have a boolean value decide between 2 values
            -- which is the same as writing 
            -- "if bright then
            --      i.Frame.Transparency = 0
            --  else
            --      i.Frame.Transparency = 0.5
            -- end"
            --but instead of "then" and "else", you use "and" and "or"
        end
    end
end

hornDebounce = false
function Honk()-- if you are reading this then congratulations! you win a prize!
    if hornDebounce then return end-- unfortunately, I could not think of a way
    if engineBlock and engineBlock:FindFirstChild("Horn") and engineBlock.Horn:IsA("Sound") then
        hornDebounce = true-- to allow people to be able to honk the horn for both PC and mobile
        engineBlock.horn:Play() -- in an unobtrusive way. Sorry! :(
        print("beep beep") -- UristMcSparks, the guy in charge of the toolbox, doesn't want print statements
        wait(0.5)-- but since this is a secret, lets keep it between you and me, OK?
        engineBlock.horn:Stop()
        hornDebounce = false
    end
end

function UpdateVehicle()-- this is for the brake lights and speed and stuff like that
    if seat.Throttle == 1 and carRunning then-- if we're going forwards
        seat.MaxSpeed = forwardsSpeed-- give it forwards speed
    elseif seat.Throttle == -1 and carRunning then-- if we're going backwards
        seat.MaxSpeed = reverseSpeed-- give it backwards speed
    else
        seat.MaxSpeed = 0 -- otherwise, give it 0 speed
    end
    if workspace.FilteringEnabled and RemoteControlled then--the idea from scripting level 2 applies to false as well
        RemoteControlled.Throttle = seat.Throttle-- that is, it also works for "~= false"
    end-- the reason this line exists is to prevent the server from doing something the client
    -- is already doing.
    for _,h in pairs (ReverseLight) do-- all these loops below are just updating the lights
        h.Enabled = lightsOn and seat.Throttle == -1
    end
    for _,i in pairs (ReverseBulb) do
        SurfaceGuiStandard(i,lightsOn and seat.Throttle == -1)
    end
    for _,j in pairs (RearLight) do
        j.Brightness = 4-math.abs(seat.Throttle)*3
    end
    for _,k in pairs (RearBulb) do
        SurfaceGuiBrightness(k,lightsOn,seat.Throttle == 0)
    end
end

seat.Changed:connect(UpdateVehicle)-- this is so that when someone drives the car
                                   -- the brake and reverse lights change
                                   -- and the speed of the car changes
CreateStabilizer()

while true do
    for i = 1, 60 do--60/30 == 2, 2 seconds between deciding if it's upside down
        wait()-- we want the steering and sfx to update as many times a second as we can
        if workspace.FilteringEnabled then
            if car:FindFirstChild("LeftMotor") then
                car.LeftMotor.DesiredAngle = seat.Steer*math.rad(20-seat.Velocity.magnitude/10)
            end
            if car:FindFirstChild("RightMotor") then
                car.RightMotor.DesiredAngle = seat.Steer*math.rad(20-seat.Velocity.magnitude/10)
            end
        end
        -- below: make sure there's a sound to play
        if carRunning and engineBlock and engineBlock:FindFirstChild("Running") and engineBlock.Running:IsA("Sound") then
            engineBlock.Running.Pitch = CalculatePitch()-- and make sure that the car is on before trying
                                                -- to make sure the engine sounds good
        end
    end
    if car:FindFirstChild("Stabilizer") and car:FindFirstChild("LeftHelper") then
        if car.Stabilizer.CFrame.lookVector:Dot(car.LeftHelper.CFrame.lookVector) < 0.85 then
            CreateStabilizer()
        end 
    elseif car:FindFirstChild("LeftHelper") then
        CreateStabilizer()
    end
    if not flippingDebounce and (seat.CFrame*CFrame.Angles(math.pi/2,0,0)).lookVector.Y < 0.2 then--am I upside down?
        Spawn(Flip)--flip the bike right side up

        -- as a fun experiment, see what happens if you replace "Spawn(Flip)" with "Flip()"
        -- and see what the difference is when you drive the car off the baseplate
        -- if you did it right, you'll notice that the engine sound changes differently!
    end
end

-- scripting level 1000000: go
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fix pls