I just used a very similar HVLP gun. This is important: Get a big can of lacquer thinner to keep your gun and its nozzle and pathways clean.
Before getting to the paint, prep your gun by putting about 2 oz. of lacquer thinner in the hopper and spray it all through into a cloth you are holding in your other hand, use the cloth to clean the nozzle's outside etc. Also, if you've used the gun already, disassemble and use the thinner to clean all the parts and put it back together, then spray the thinner through it.
After that, the key is thinning the paint with clean water (bottled) until it is the consistency of heavy cream, it'll be quite runny (almost watery) and that is what you want. Again, getting the paint thin enough is key to eliminating your problem.
Make sure you have at least a 15-20 gal compressor or you'll have a lot of down time waiting for the compressor to catch up.
Now, load your thinned paint into the hopper and test/adjust the "fan width" (using some scrap) to about a 10-12 inch span. The fan width should be top to bottom, not side to side. Make sure to also practice your painting stroke from side to side. You want to start the spray stream just before you make contact with the cab spraying uniformly from side to side. Keep the spray gun about 8 inches away from the surface. Each pass back and forth should be like mowing your lawn....as you move along, make sure the next pass crosses by half, the pass before it to get proper blending. Don't worry about "lite spots" as you will want to apply at least 2-3 coats. Make sure each coat goes on criss-crossing the direction you went on the prior coat. So, if you went from top to bottom on the cab the first time; on the next coat go from side to side.
Do a light sand (I used 220 grit) in between coats for a great sheen.
This is very important. After each coat, CLEAN your gun and it's parts with the lacquer thinner and repeat the process from the beginning, spraying a bit of lacquer thinner through the gun before loading the hopper with the next batch of thinned paint.
Also, as your painting, keep a wet cloth in your non-painting hand and frequently wipe the nozzle tip between passes as you paint. This prevents dried debris on the tip from flying onto your paint job.
For painting I placed the cab on its side spanning a couple saw-horses with towels on them. This allows easier painting and it eliminates runs. You may get some pooling if you linger in one area too long so make sure you keep your strokes consistent and moving.
Hope this info. helps.