The only real way to clean them out is to send them to a place that will balance and blueprint them. They put them on a machine that sprays them while subjecting them to ultrasonic vibrations. This brings them to a better than brand new state.
Otherwise you can take some brake cleaner and spray out their little filters, pulse them with a battery while spraying them at the tips, but it really only cleans the surface and you'll be back to square one in less than a year.
Also take off your intake manifold so you can clean out the injector passages.
http://www.rceng.com/Fuel-Injector-Clea ... lQg9EzKJbT