Hello, The cap venting can be a challenge! I’m still a beginner, just a few months and always trying to see how this could be better and I found what works for me is to try everything; adjustments, liner widths, speed and stroke combinations but do it slowly in small increments. You have the time! Today I edged for 4 hours using a new technique that kept the cap on at almost all speeds and lengths by changing the stroke by way of sucking very hard on the air box hose w/o the air box for a longer stroke and locking it where it feels right for 1 minute or 20, always changing the squeeze pressure and stroke by using a plastic hose clamp like an enema hose and the speed. Endless combinations. Do you want a shorter stroke; just loosen the clamp a click or two, a little more and I’m getting the best head suck job around. I have fun with it! I made a camera video today of it stroking attached to my desk with a brass cup hook screw and a small zip tie and rubber band. It stroked great for as long as I wanted but I don’t know how to post a video here. I’ll figure how if anybody wants to see it.