To eliminate the orange peel with the primer, sand you primer with some 2400 wet dry paper. Just to take the upper edges off of the primer, and the put your color coat. Either that or switch to a different primer.

I just airbrushed Vallejo Grey on a '69 Dodge, with the intentions of the Scale Finishes Dodge Butterscotch for the top coat. Only thing about the Vallejo primers, you gotta let it sit for 4-5 days before you can sand on it, as it will just peel up before it is cured. Although I have done it sooner than that, you just have to have lots of water for lubrication and hit with 3600 grit or so.