Good luck with that setup. You need to provide a vent of some sort to allow air INTO the engine. Generally, it goes into the valve cover, and pulls back out of the crankcase somewhere, but you might be able to create some sort of metered opening in the draft tube by welding the pipe partially shut, and using the airflow backwards to the normal route. (In at the crankcase, out at the valve cover) Definitely don't block off the breather tube altogether, as you'll create a vacuum in the crankcase that will cause problems. The idea is to flow air through the engine, not seal it off and make a suction on it like a can of soup!
Jerry
