Hi you may need to take it to a garden machine specialist to get it fixed. it could be the coil pack is no longer working.

Thanks for all of the advice folks, sometimes the simplest answer is the best. I shall change the fuel and measure more exactly, but I don't think I'll be turning it into a go car lol.

Most likely the fuel/oil mix is wrong.

Add more oil to the fuel. Your not using the right ratio.

unglog the cooling fan cover then.