Yeah I would try turning up the pressure a little. You really should get a regulator for the gun though. After experience you will sort of be able to guage your pressure without even looking at the guage, but you still want to be able to regulate it at the gun. They are not totally accurate, but should give you an idea where you are at. Yeah I have a zhipp gun, different model, and it is advertised as hvlp, but really isn't an hvlp gun. I think I shot around 50 p.s.i with my gun on the last coat of urethane clear and it shot well. but you have to find your own setting, different gun, urethane paint. Mine layed out well for me.
I think you should be able to spray enamel with a 1.4 tip. Been many years since I've sprayed enamel, and it was mostly conventional guns with around a 1.6 tip, binks 7, devilbiss, ect. If airpressure doesn't improve things, you may try over reduceing it a little to get it to spray better, or if it doesn't call for reducer, buy a decent grade of enamel reducer and add it in and see if your results improve, probably medium or slow reducer depending on temps. I wouldn't overreduce much more then 10% though. Most hvlp guns still call for fairly high pressure going into the gun to spray well, the gun itself reduces the pressure inside to give complient pressure at the aircap. But there is such a wide range of pressures people set there gun at depending on what they have. I've read some say as little as 23 pounds inlet pressure on here, My accuspray hvlp I set somewhere around 40-50 lbs inlet. There is usually a max air pressure rating on the gun body, or should be in the manual inside the box. If you over pressurize too much, not sure what would happen. I think mainly would blow out seals.