Likewise, I almost always just go ahead and install the vent line though I'm a fan of the balsa box termination rather than just running the line into the fuselage. On a couple of planes that had problems, just running the line back into the fuselage had almost zero effect on the problem so it was clear the whole fuselage had pressure issues. I fabricated a small balsa box with a single pinhole in it as RTK who use to be on here suggested and problem solved. The line just terminates to a piece of brass tubing glued into one corner of the box and the box is retained in a convenient location by Velcro.

I still feel it is necessary for a gas engine newbie to know the possible causes of why his engine is running so poorly in the air when it runs great on the ground.

I think the unique red regulator cover that DA uses on some of their engines is an interesting approach to resolving the problem. Likewise, the 3W vent line to the intake area.