Clear return line to see bubbles
 

My inj. return lines were cracking, so I got some translucent fuel line from the mower place, to see how tight the whole thing was. Well, I there are a lot of air bubbles in the return lines. The material is harder than normal, maybe not a good seal? The fuel filter has only a very small bubble in it. The vehicle runs well, are these bubbles a problem? There is quite a bit of air, even after running hard for a while.

You mean the 1/8 inch injector return lines rather than the IP return line, correct?

I had clear lines on my injectors for a quick fix a couple weeks ago and they too had bubbles in them. However I didn't try and prime or purge the system after replacing so the bubbles could have been stuck. As long as the car is running well I wouldn't worry about it. You'd know when you have a lot of air going through your feed lines.