I have removed the two bottom screws next to the Zinc thing above the prop and have removed the screw at to front of the lower unit. I have some pivoting movement, but haven't figured out how the lower unit comes off. There is one other screw that has a plate and is where the intake screen is, but I have unscrewed it for five minutes and it doesn't appear to have moved a millimeter. Does this screw half to come out also or this there some type of twisting thing I have to do to remove the lower unit?