Kris
From my own experience, your problem may be one (or more) of the following:
1. A clogged airbrush;
2. Pressure too low; or
3. Ambient temperature too low.
Solutions may be:
1. Clean after every spraying. Alternatively you may be using an internal mix brush when a cheapo external mix (e.g. Badger 250) would do a better job;
2. There is no proper substitute for a compressor. If you're using canned propellant, dunk it into a jug of warm water while you spray. If you're trying to use an inflated car tyre, give up.....there's no point in being a damned fool for a model boat, is there? Save up for a compressor and buy it ASAP. I left it about twenty years too long.
3. This one's easy...........but suit yourself anyway, eh?
Never tried the brand of paint you mention so I can't comment on that. Don't chuck it away, however - Testers would be bankrupt if it was no use to anyone!
Good luck
FLJ