can i still use these? the little black plastic piece on the bottom of 2 are missing....

 

I am under the impression that the plastic is around the bottom of the injector in order to protect the injector pintle, so as long as the pintle isn't damaged, I dont see why you couldn't use them. On one of my 450s I think there was a small piece that had come off like yours on one and I installed it anyways and never had a problem.

 

ok. i thought it had to do with evening out the spread of the spray.