Silencers massively affect performance.
There is a dark art to them that even I don't understand, something to do with pipey engines liking long stingers.
Graham Bell's Two Stroke Performance Tuning would probably have the answer. Highlighly recommend this book
Oil dripping from the Exhaust pipe is normal. Two strokes are oil machines.
Back pressure is essential for two strokes, something to do with the harmonics of the sound wave created. But I'd be lying if I knew.
You will have to refer to a proper text book in order to gain a proper understanding of pipes. I'm afraid my knowledge is dicey at best.
