Gas will not ignite!?

Hi, Firstly thanks in advance for any help, secondly I cannot beleive it is possible to have thousands of questions regarding gas cookers as there seems to be on this site. Anyway here is mine;

I have a cooker with four gas rings/hobs on the top. Three work fine, one doesn't. The one that doesn't work does have a gas supply and the gas flows through fine when you turn the valve, but strangely enough the gas will not light, and I use a flame not an ignition spark. I took off the cover to the hob and I can see the gas jet injector with the hole in the centre. When I compare this one to one of the hobs which does work I notice that the hole in that one has a much larger diameter even though the hobs are the same size. Should I replace the jet/injector with one with a larger hole? Can a too small hole really cause this problem?