I think perl_geek is closest: you need a skirt (like all hovercraft have). But also, I don't think it is cheating to have 4 tiny low-profile wheels spaced 90 degrees apart, to keep the leaning platform from nose-diving and biting into the pavement, thus spilling our Max in a most MAXimum way. By leaning, the leaking air will provide just a bit of thrust, at the expense of altitude on the leading edge (thus the need for the protecting wheel). Want more, just remove the governor (?) if it has one. If it doesn't, then shave the cylinder head to increase the compression; but watch out, it will get very hot, so you will need to adjust the fuel. Oh and by the way, the engine could spit its shaft, so have a metal plate between the engine and you. Just a thought or two.
For a practical hovercraft, (using a rather loose definition of "practical"), a flexible skirt is vital. Apart from increasing the ground clearance, and sealing the airflow, lifting panels can be used for control. Depending on the proportions, pressure, &c., control might be possible simply by titling the platform. Leaking air and Isaac Newton do the job.