[cleszkie]

If I'm not mistaken, the whole purpose of the PVC valve is to control when crankcase gases are introduced into the carb. At wide open throttle, or under loads, the manifold vacuum drops dramatically. Sometimes all the way to zero inches of Hg. This drop in vacuum prevents the PVC valve from openning, and thus the carb is only fed clean outside air during these times of heavy load. The PVC valve only opens during cruising speeds when the engine is producing enough vacuum (15 to 20 inches of Hg), and there is no big load. The engine can then consume the crankcase gasses without noticeable impact on performance or power.

By not having a PVC valve between your oil fill tube and the carb, you are feeding your carb crankcase gasses all the time, and this is affecting your wide open throttle and under load performance/power. The engine designers knew what they were doing when they introduced the one-way vacuum controlled PVC valve system. I suggest installing an in-line PVC valve between your oil filler tube and carb.