So I found these on moped army. (Under wiki, subsection performance, first paragraph recommend reading) I hope admin can make this a sticky thread? http://3cyl.com/mraxl/manuals/bell/performance-tuning-graham-bell.pdf The bell book is amazing. I've learnt a lot from it. There is a four stroke tuning book by him too if I recall. http://www.vintagesleds.com/library/manuals/misc/Two-stroke Tuner's Handbook.pdf This one I haven't really read yet, just skimmed. Seems a little less in depth than the bell book.