when installing say 1000cc precisions they come with a big rubber o ring. now, do i use just that o-ring or do i put the oring on, then press them into the injectur grommet

 

Well I'm guessing the big o-ring you're referring to is the one that goes into the intake manifold. I don't know about your precision 1000cc's, but w/my rc 440's when I pulled the stock inj., those o-rings stayed in the intake mani and I just left them there and used them. No leaks. If you're talking about the small o-ring for the fuel rail, you can use either the one's that come with, or carefully peel the o-rings off of your stock inj.

 

^ true the same thing with my 680cc's left the origonal gromet in the intake. no leaks yet, at least not from there.(------ peice of ---- fuel rail!)