I have a PC 260C Finish nailer (2 1/2" to 1" length OK) with 1 1/4" Dewalt brads. Air compressor set on 80 PSI. Brads fire erratically if at all. More than half jamb. Sometimes 2 pins.

SOURCE: Nailer jams with 1-5/8 brads

It sound to me that the 1 5/8 brads are not 18 guage but probably 16 guage and they will not work. Double check them first before going any further. You can usually lay them next to the smaller ones that work and see the size difference, if not let me know and I will dig deeper.

SOURCE: New Porter Cable BN200A brad nailer won't fire.

I have seen this problem several times and have been able to repair like new by replacing part #894737 head valve seal. Upon assembly examine metal parts for fine scratches where orings or seals contact. Remove scratches with fine sandpaper (300-400 grit). Lube orings/seals with silicone lube sold at Lowes in the plumbing department (Danco Brand). You can buy this part from local Dewalt repair center or on the net at www.toolpartsirect.com. This part is alco included in kit #60061. Install the kit if gun is several years old or has lots of wear. This nailer will not operate correctly if there is an air leak. If you have a leak after installing new part/parts please email for directions. Good luck!

SOURCE: New Porter Cable BN200A brad nailer won't fire

Go to this site: portercable support page:

http://www.deltaportercable.com/ServiceAndSupport/ServiceAndSupport.aspx

SOURCE: nail gun wont fire

First - the air pressure has to be high enough - check the regulator on the tank to make sure it is delivering in excess of 60-70 psi (which I am sure you have already done).

If you have dry fired these guns (i.e. shot them off with no nails in them while you were lubricating them maybe) the mechanism inside could be damaged. I had that happen to one of my nailers (same brand). That was when I learned not to dry fire them...

Since both of them are not working though I would be more inclined to look at the air supply first.

SOURCE: BN200A porter cable brad nailer. have tried

check for a broken driver blade, also make sure of the proper nail guage for the tool. Let me know if this is not the case and I will find you a breakdown for the tool for further inspection.