Originally posted by Sixt9coug
my 2 cents here... ( new guy 2 cents lol ) 400 grit is too fine for primer to stick too well. i would at least use 220 wet and do the whole car with that and a red Scotchbrite pad. masking is key as well. laquer primer in my experience sucks. get a primer that will require a hardener with it. ( PCL Polyprimer is a fav of mine and isnt hard on the wallet... $60 or so a gallon.. not really for flexible parts like bumpers though ) my first gun was also an HVLP Harbor Freight gun and well i still have it and it still works as well. for heavy duty primering i use my Sharpe Cobalt HVLP. it has a 2.3mm tip on it ( auto body guys know... that gun doesnt **** around lol ). it was about $130 on Ebay. the Harbor freight one is about $50. i spray primer at about 30 psi as well. so i agree with that above. well....... thats a start to doing it.... have fun. i love painting 
2.3 mm
Thats a big tip. That's ideal for primer surfacer. Is that what you use it for?