I bought this Vaccum Engine (aka flame-licker engine, flame-engine, flame-dancer) on Ebay.

Although obviously produced commercially it didn't work.

I adjusted the linkage of the engine, opened the intake from 6.5 to 9.5 mm and reduced the diameter of the piston slightly.

After lubricating it with Molybdenum Disulfide (MoS2) powder it worked.