The jets are very probably blocked with limescale deposits from hard water - pushing a pin in the hole may clear it but it only pushes the crud back into the tubes so it can block again.
I use half a cup of Viakal in the tank and a top up with water - sometimes it clears in 20 minutes but more usually 24 hours - others say Cillit Bang works but it didn't for me.
Viakal goes in very easy - much easier than taking the car apart.
Good luck...
Peccavi
January 2010