Is it 2-stroke or 4-stroke?
In the US, one popular adaption of simple, 2-stroke engines originally designed for methanol or gasoline is to what we call "gas-glow." Methanol fuel is $14/gal and up. Gasoline is now about $2.25/gal.
If the engine is a 2-stroke and originally designed for gasoline/oil and spark ignition, then add about 10 to 15% model airplane fuel, and it should at least start popping with a heated glow plug. You need to be sure the oil mix is no lower than when it ran on gasoline alone (usually 1:20 to 1:50). Most American gasoline now has 10% ethanol in it. What we call "marine" gasoline is ethanol free. I would use petrol without ethanol.
If the engine is 2-stroke and originally designed for methanol-based fuel, converting to gasoline is not a big deal, but you have to be mindful of the connecting rod bearings. Such model engines will almost always have just plain bearings and are designed to run with 10% (minimum) oil, so you must increase the oil to 10% or more when running with gasoline.
If it is a 4-stroke engine, the same considerations as to its original design (i.e., gas or methanol) must be taken into account. Plus, you need to consider plug cooling. Converting such engines to gas-glow is not done that often in the US. I suspect you may need a 4-stroke glow plug, which is designed to stay hot better, and you may need electrical heat at higher rpm's or even continuously to get a good running.
John