It’s easy enough job. Remove the windscreen wiper arms, one nut for each. Remove the two oval caps covering the screws that hold the plastic scuttle in place and then remove these two screws. You now need to release the plastic pins that hold the rubber seal at the front of the scuttle, a pair of needle pliers make this easy. Once all the pins are out jiggle the scuttles and they will come away giving access to the jets. Give them a clean and a blow through and all should be well. There is a ball bearing and Spring valve that sticks. This sounds much worse than it is,
Two things to note. You will almost certainly snap the little clips off the oval covers for the screws so unless you are rearly lucky these will need replacing ( I just taped mine in place with black electrical tape until I put an order in for other stuff from mx5 parts ) and while the scuttle is off seal the grommets that the screws go into. They are know to leak and cause problems.
Good luck.
D
When refitting the scuttle, watch out for the hooks which hook under the front edge of the windscreen.
They are not particularly troublesome, and dont have to clip on to anything, but it’s easy to fit them sitting on top of the glass instead of underneath it.