So, the output doesn't say anything and I don't know whats wrong... :c
function drive ()
local speed = script.Parent.Speed.Value * 100000 + 100000
script.Parent.MainPart.BodyForce.force = Vector3.new (speed,0,0)
end
script.Parent.Speed.Value.Changed:connect(drive)

5 comments
Are any of the parts anchored?
nope
Make the number an insane number. Maybe math.huge. If this doesn't work then their is probably a structural problem.
Oh, if it does woork, then it's because you're not using enough force with the shown script.
I even tryed changing the "speed" value to something like 99999999 to see if it would be too slow and.. Well nothing happened.