Just cleaned off my four oil spray jets in the parts washer, but I can't be sure that they are clean. You can't see any light coming through from one end to the other, even though I'm sure they are free of oil now. I tried inserting a bristle from my brush and there's definitely a 'stop' in there from both ends, on all four jets. Anyone know what the internal design is, and how I can check that they're free of debris and ready to work correctly?

 

The Bore Squirters have a built in spring loaded check valve - this check valve prevents the oil flowing through until the oil pressure reaches 57 psi.
I normally soak the Squirters in solvent/carb.cleaner and then gently blow them through(from the threaded end) using a compressor and an adjustable regulator so you can slowly increase the air pressure to see they are opening.
You will see the solvent being sprayed out of the jet to confirm they are working.

 

Thanks Mick. Luckily I'm having a compressor off my brother in law soon so this will be another potential use for it!