I am repainting my 73 F-100 and had a problem. I did the bodywork on the bed, primed, and sealed. I am painting the truck with acrylic enamel single stage paint. I am using a TP turbine hvlp sprayer. I did the 1st coat and it turned out great. I waited until it was not tacky and did a second coat. I took a drop light and looked down the side real close and it looks like there are millions of pinholes in the paint where the primer is exposed. This is only noticable with a light looking very closely. I think maybe it was too cold. It got between 50 and 60 degrees outside, and I was in the garage with the door cracked. Anyone who could help me I would appreciate it. And do I need to wait and spray another coat??? Thanks

 

boy it sounds like solvent pop. Reference: Solvent Popping - Troubleshooting
Only other thing else I could think of that would look similar is either fisheyes/paint extra thin, or water contamination. But from you description and the fact it occured on the second coat, I would think most likely solvent pop.
Maybe you got solvent buildup due to it being cold along with using a turbine sprayer. I haven't used a turbine, but have heard they can cause some trouble too cause the turbine heats the spraying air.
Maybe the combination of cold weather and surface (cold or humid weather will slow down solvent escape), along with the heated air which caused the paint to flash off too fast (top skims over too soon, and then the solvents which haven't had enough time to excape, break the surface when trying to escape, first causing bubbles then when popped, tiny little pinholes) trapping the solvents. Not positive that was your problem, but its my thinking and what came to my mind.
I would think it would have to do with trapped solvent when applying the paint, not ones that got trapped down in the primer coats, due to it occuring on the second coat of paint.
Unfortunatly, if its solvent pop, you will most likely have to sand down far enough to get rid of the holes, and repaint.
Here is a link to a discussion on turbine sprayers in a quick search I did, but its from a site dedicated to wood finishing and paint, not automotive.
Heat Problem with a Turbine Sprayer

I don't know what reducer you used but you may want to try a slower speed enamel reducer if you used fast, and allow a good amount of time between coats, and if possible spray in warmer conditions.

 

I use a 4 stage turbine along with an Accuspray gun and my instructions said to use more reducer than called for by the paint manufacturer due to the heated air. So my Concept CLV says to use 5-10% by volume I will go up to 15% by volume. On the other hand when using the DPLF I haven't had a problem spraying it without any reducer within the basic temperature range. I learned that on the color coat back in 1991 when I sprayed my first car with a turbine system. Only my problem was orange peel because the paint didn't flow out like it should.

 

Thanks for the info. I am going to sand down and spray today. It is supposed to be around 78 degrees today. I will allow more time than usual to let dry. Thanks for the help again.