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Oh, yeah.....we are all familiar with that delamination here. Sounds like you already know this since you are talking primer.....you've got to go all the way down to bare metal when you are experiencing that.
Okay, on guns/tips.... First, I cheat....I use a crappy old regular compressed air primer gun with a 2.0 tip. It hoses on primer. Now for base and clear I do indeed use my turbine guns. Tips I have are 1.0, 1.2, 1.3 and a 1.4. I think for base you could use your 1.3 and since that's all you've got there it should be okay for the clear. You could use the 1.8 for primer for sure since you've got it there.......

Yes I've seen you mention before you apply the primer with your conventional gun. I could go this route too, I have several cheap compressor guns but none with a big needle yet. Also I only have a 21 gallon 2.5 HP compressor (5.8 CFM @ 40 PSI, 4.7 CFM @ 90 PSI).

Sounds like I might find myself needing a 2 or 2.5mm needle for primer if I try it with HVLP. Besides the 1.3 & 1.8 that I have what other sizes might be good to have for the base & clearcoat? Was thinking maybe 1.5

Fuji Tip Options
#1 - 0.8mm
#2 - 1.0mm
#3 - 1.3mm
#4 - 1.5mm
#5 - 1.8mm
#6 - 2.0mm
#7 - 2.5mm

Yeah, compressor is definitely underpowered. Since it is just primer though, you could section it out, maybe. Your 1.8 should work fine with that turbine and primer though.... On the tips yeah, 1.5 might be handy but it could be a little more "peely" with that 5 stage. Honestly, though tip size is not quite as critical with turbine systems.