Small Engines (Lawn Mowers, etc.): for my research project, gasoline engine, cylinder engine

Question
may i know how methane is used as fuel for small engine, one cylinder engine, 5.5Hp?
how to convert this gasoline engine into methane powered engine?

Answer
I have never seen a small engine run on methane.  The only way I could think of making this work would be to start the engine on gasoline and then changeover to methane.  Methane being gaseous, will act differently when mixed with air.

Theoretically you could build a pressurized fuel system where the engine would not use atmospheric pressure.  I would suggest looking at a car that runs on natural gas.  A methane system would have to be very similar.

I know this doesn't answer your question very well but it's the best I can think of.  Good luck on your project let me know how it comes out.