I wouldn't mess with the tube. I don't remember there being much crud in either one of mine, and the box and flame trap on the 245 were unbelievably vile. The s-tube between the flame trap and the box was about 3/4 clogged, and the box felt like it was filled with lead fishing weights. It turned out I had a leaking headgasket that was letting combustion chamber stuff into the oil galleries--no wonder there was carbon everywhere.

My understanding of the box's purpose is that it's meant to give cruddy oily vapors a place to separate into their three component parts: oil that runs down the tube to the sump, air that gets sucked into the intake, and carbony crud that builds up in the box. The crud should stay in the box, not go down the tube.

John